Question: I am a father of a 10 years old boy and sending this question from Bangkok, Thailand. I need solutions for the following:

1
Joseph and Peter spent $45 altogether.
Joseph and Harold spent $65 altogether.
If Harold spent 3 times as much as Peter, how much did Joseph spent?

I know the answer is $35 but do not know how to get to it.

2
Ron bought 3 notebooks and a newspaper.
He paid $30 to the cashier and received $5 change.
If the newspaper cost twice as much as each notebook, find the cost of the newspaper.

I know the answer is $10 but do not know how to get to it.

3
Paul has twice as many stickers as Andy.
Andy has 40 more stickers than Lily.
They have 300 stickers altogether.
How many stickers does Paul have?

I have no idea how to get it.

4
The total weight of Peter, Dan and Harry is 123 kg.
Peter is 15 kg heavier than Dan.
Dan is 3 kg lighter than Harry.
Find Harry's weight?

I have no idea how to get it.

I thank you very much for your kind help
Regards
Oliver

Oliver,

I will do one of the problems for you to give you an idea of a way to solve them. I am going to use algebra as I expect that is what is expected. Here is a solution to problem 4.

Let P be Peter's weight, D be Dan's weight and H be Harry's weight, all in kilograms. The three statements in this problem then can be written as equations

The total weight of Peter, Dan and Harry is 123 kg.

P + D + H = 123

Peter is 15 kg heavier than Dan.

P = D + 15

Dan is 3 kg lighter than Harry.

D = H - 3

I want to obtain one equation with only one letter (variable) in it. In the first equation I ca replace P by D + 15 to get

D + 15 + D + H = 123 or
2D + 15 + H = 123

The third equation is D = H - 3 so H = D + 3. Hence in the equation above replace H by D + 3 to get

2D + 15 + D + 3 = 123 or
3D + 18 = 123.

Subtract 18 from each side to get

3D = 105, and thus
D = 35 kg

But you want Harry's weight which is 3 kg less than Dan's weight so Harry's weight is 32 kg.

Penny