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Working backwards 2015-08-27
From Heather:
Tom took a collection of tiles from a box. Sue took 13 and Bob took half of those remaining. Tom had 11 left. How many did they start with?
Answered by Penny Nom.
How many boats total are in the marina? 2015-04-15
From Carla:
In a marina, 3/4 of the boats are white, of the remainder 4/7 are blue, the rest are red. There are 9 red boats. How many boats total are in the marina? My answer is 84 because if 1/4 of the boats are divided into sevenths, that makes the whole marina a 28 part item. 3/28 are red so 84 is the total number of boats. My child thinks I am wrong.
Answered by Penny Nom.
Mary gave her sister 5/8 of her nuts 2015-01-22
From Valence:
Mary gave her sister 5/8 of her nuts. Her sister gave her friend 2/3 of the amount, and her cousin 1/3 of the remainder. If Mary's sister had 50 nuts left, how many nuts had Mary.
Answered by Penny Nom.
Grandpa had an apple tree 2014-09-14
From Emma:
Grandpa had an apple tree. On the first day half of the apples plus one fell to the ground. On the second day, half of the remaining apples plus one fell to the ground. On the third day, half of what was left plus one fell to the ground. The tree was left with only one apple now. How many apples did the tree produce originally?
Answered by Penny Nom.
Brandon went shopping - working backwards 2014-07-11
From Sindy:
Brandon went shopping & spent 1/4 of his money on shoes & 1/5 of the remainder on a new wallet. He then spent $60 on a pair of jeans. If he had $60 left, how much did Brandon start with?
Answered by Penny Nom.
Working backwards 2013-07-28
From Petal:
Tom bought some oranges. He threw 37 rotten oranges and bought 56 more. Finally he had 220 oranges. How many oranges did Tom had at first?
Answered by Penny Nom.
GST in New Zealand 2012-10-10
From Colleen:
I work out my claimable gst each month but need to know the total sales or purchases amounts for filling in my six monthly paper work. How do I do that. I tried doing the opposite of calculating the gst i.e. x3 and /23 but it is slightly different to my total.
Answered by Penny Nom.
How many oranges? 2012-10-06
From Rodger:

Question from Rodger, a teacher:

How Many Oranges?
Marjorie, Colleen, and Bob picked oranges together. They were tired after picking a large number of oranges and so fell asleep. Marjorie woke first and decided to take her third of the oranges and head home. She counted the oranges, and found that the number was divisible by 3 if she took one of the oranges first. Marjorie took one orange and then took one-third of the remaining oranges. She left quietly.
Bob awoke a short time later, noticed that Colleen was sleeping, and presumed Marjorie had gone for a walk. He decided to head home because he wasn't feeling well. Not realizing that anyone had left, he counted the oranges and found that the number of oranges was two more than a number that could be easily divided by 3. So he took the two extra oranges and then one-third of what was left. He left without waking Colleen and without waiting for Marjorie to return.
Colleen finally awoke and wondered where her friends had gone. She assumed they were both busy somewhere nearby. Before she left, she counted the oranges and was surprised at how small the number was. She found that the number of oranges was one more than a multiple of three, so she took the extra orange and one third of those remaining.

1. What was the total number of oranges the friends picked?
2. How many oranges were left behind when Colleen departed?
3. Is more than one answer possible for the total number of oranges? If so, what other numbers are possible? Explain.
4. Based on the values you found in problem 3, determine a reasonable solution to the problem. Explain your answer.
5. Is it possible that five oranges remained after Colleen took her share? Explain.
6. Could there have been six oranges left after Colleen departed? What about 46 oranges initially? Explain
7. Find a pattern that gives all the possible numbers of oranges that the friends picked. Explain your pattern

5. Is it possible that five oranges remained after Colleen took her “share”? Explain. 6. Could there have been six oranges left after Colleen departed? What about 46 oranges initially? Explain 7. Find a pattern that gives all the possible numbers of oranges that the friends picked. Explain your pattern

Answered by Penny Nom.
Problem solving 2011-10-27
From keelan:
a number is divided by 5. then 3 is added to the quotient. after subtracting 10, the results is 30.what is the number.t
Answered by Penny Nom.
Working backwards 2011-03-10
From Kevin:
Duwayne wrote a two -digit number.He multiplied it by 3,added 18, and divided by 8.His final answer was 9.What number did Duwayne write
Answered by Penny Nom.
Working backwards 2010-06-22
From Martha:
Karen spent all but $8.00 of her savings in three stores. In each store she spent $2.00 less than half of what she had when she went in. How much money did Karen have at the start.
Answered by Robert Dawson.
Working backwards 2010-04-11
From adel:
alice gave reggie and freddie as much money as each had already.reggie in turn gave alice and friddie as much money as each already had in negotiable treasury notes. freddie gave alice and reggie as much money as they each had. in the end they each had the same sum, 24000.00.how much money did they each in the beginning?
Answered by Penny Nom.
An afternoon at the races 2009-05-15
From garths:
A professional gambler was betting at a horse racing afternoon.
At the end of the first race he had doubled his money.
He bet R30 on the second race and tripled the money he came with.
He bet 54 on the third race and quadrupled (4 times) the money he came with.
He bet R72 on the fourth race and lost it all. But he still had R48 left.
How much money did he take to the race track?

Answered by Harley Weston.
$65.09 is 70% greater than the average price 2009-04-11
From Kelly:
Hello! I know you might be thinking that I didn't look through your previous answers, but I really did. Here's my dilemma- I have a percent increase equation that is missing the 'old" value. I know that $65.09 is 70% greater than the average price, but I do not know the average price. How do I go about finding that? I tried to set up an equation, but its throwing me off because the unknown variable is in there twice, and it's been a long time since I've taken math
Thank you for your help...greatly!

Answered by Penny Nom.
Marcia's summer earnings 2009-03-11
From Yasmine:
Marcia saved money by working over the summer. Before school started, she spent 25%of the money of jewelry and then 2/3 of the remaining money on a digital camera. She still had $213 left. How much money did she have before she started shopping?
Answered by Robert Dawson and Penny Nom.
A bag of coins 2009-01-09
From marina:
I have a bag of gold coins. I give 1/8 to mother then gave 1/2 of what was left to my brother i give 2/7 of what was left to father. If i have 25 coins left. how many do i have originally.
Answered by Robert Dawson and Penny Nom.
A game for 5 players 2008-11-16
From safdar:
five players agreed that after every game, the loser doubles every body's money. they played 5 games and everybody lost once. after the 5 games, everybody had 4128. How much money did each of the players have before the game? show your work.
Answered by Janice Cotcher and Harley Weston.
Fibonacci numbers 2008-01-30
From Beth:
You've answered a question for a Linda Bach on Oct. 25, 1999 that has to do with a pet rabbit and stairs. (Working Backwards) We were wandering if there is a formula we can use to plug the numbers in? My 7th grader got that exact same problem. I've spent several hrs trying to come up with a formula. I've tried the combinations formula, the Pascal's triangle and the Permutations formula. It seems like it is something real close to those, but can't quite get anything to work. What kind of formula would work for finding the outcome of this problem? Thanks so much for your help. Beth
Answered by Penny Nom.
Ridingcap's daughter 2006-10-23
From Marcus:
Ridingcap's daughter,whose real name was Coleen, set out for grandma's house again. This time she was delivering jam and jellies. First she stopped to see Mrs. Parsley,who took in grandma's mail while grandma was @ the hospital recovering from the wolf. Colleen gave Mrs. Parsley one third of the jars in her basket. Then Colleen set out again,and suddenly the wolf jumped out behind the bush and grubbed one half of the jars in Colleen's basket. When the wolf ran off, Colleen went on and gave Mr .Woodsman two thirds of what was left in her basket. Colleen had six jars of jam and jellies left for grandma. HOW MANY JARS DID COLLEEN LEAVE HOME WITH
Answered by Stephen La Rocque.
A bicycle ride around the local lakes 2006-05-11
From Geecee:
Yesterday I went for a long bicycle ride around the local lakes. As the ride was quite long, I rode in various stages. In the first stage I rode half of the overall distance. Stage two saw half of the remaining distance plus 35 metres covered. Stage three covered three-quarters of the remaining distance. Stage four completed half of the remaining distance plus 75 metres. Stage five completed the journey with a final burst of 150 metres. How far did I cycle in total?
Answered by Stephen La Rocque.
How many passengers boarded the plane in Phoenix? 2005-11-03
From Vish:
Passengers boarded a plane in Phoenix. In Dallas 1/2 of the passengers got off and 4/5 of the original number got on. In Memphis 3/4 of the passengers got off and twice the number of remaining passengers got on. In Chicago 2/3 of the passengers got off the plane leaving 39 passengers. How many passengers originally boarded the plane in Phoenix?
Answered by Penny Nom.
What number am I? 2005-10-27
From Samantha:
First 8 is added to me, then I am multiplied by 6. Then 40 is subtracted from me. Finally, I am divided by 10. The result is 11. What number am I?
Answered by Penny Nom.
Red riding hood 2004-02-14
From Frank:
Red riding hood had a number of jars to take to grandma's house. As she traveled she gave away 1/3 of them to an old lady. Then later As she walked through the forest a wolf stole 1/2 of her remaining jars. When she arrived at grandma's house she gave her 2/3 of the remaining jars. She kept 6 jars for herself. How many jars did she start out with.
Answered by Diane Hanson.
Working backwards 2003-03-14
From Melody:
Triva went to the ardcade at the state fair to win some goldfish. She already had some goldfish at home, but wanted more. She won enough goldfish to double her stock. Her mom made her give four away. She put her new ones in the tank with the others, by the morning half of the goldfish had died. Triva's friend gave her six more. The next morning two-thirds of her goldfish died. She was left with two goldfish after giving one to a friend. How many goldfish did she start with?
Answered by Penny Nom.
Dorothy and the wizard 2003-01-24
From Ken:

dorothy was going to see the wizard of oz...she stopped at the bakery and bought a box of cookies.

she met the scarecrow and gave him half the cookies. she ate half of the remaining cookies and threw one half cookie away.

she met the tin man and gave him half the cookies. she ate half the remaining cookies and threw one half cookie away.

she met the lion. she gave him half of her cookies. she ate half the remaining cookies and threw the LAST half cookie away.

how many cookies did dorothy leave the bakery with?


Answered by Penny Nom.
Tonya in the orange grove 2001-04-25
From A parent:
Tonya was helping in the orange grove. She decided to take some oranges home to share with 3 friends. She gave 3 more than half to Jennifer. Angela got half the remainder and 3 more. She gave Josie half the remainder plus three. When she got home, she had only 10 oranges left. How many did she have when she left the grove?
Answered by Penny Nom.
A bargin with the devil 2001-03-21
From DJ:
There once was a boy who spent all his time dreaming about getting rich. " I would do anything to be rich". The devil, hearing this, appeared before the boy and offered to make him rich. "See that bridge?" said the devil. Just walk across and I will double your money you have now. In fact, each time you cross I will double your money. There is just one thing you must give me $24 after each crossing. The boy agreed. He crossed the bridge, stopped to count his money and, and sure enough, it had doubled. He paid the devil $24 and crossed again. Again his money doubled. He paid another $24 and crossed a third time. Again his money had doubled, but this time there was only $24 left which he had to pay the devil so he was left with nothing. The devil laughed and vanished.
  1. How much money did the boy start with?

Answered by Penny Nom.
A merchant from Pisa 2001-02-11
From A student:
A merchand doing business is Lucca doubled his money there and spent 12 denarii. On leaving, he went to Florence, where he also doubled his mone and spent 12 denarii. Returning home to Pisa, he there doubled his money and again spent 12 denarii, nothing remaining. How much did he have in the beginning?
Answered by Claude Tardif.
Working Backwards 1999-10-16
From Linda:
I am having problems finding examples of problems that require "Working Backwards" used as a strategy for solving. We are required to give a presentation on Monday, October 25, 1999 in our school districts math class. We are trying to become better problem solvers and how to teach problem solving in the elementary classroom. Help! I can't find anything in my web searches.
Answered by Penny Nom.
 
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