Niece has a question that was marked wrong but we are unable to determine how the teacher calculated and arrived at the answer? The problem was as follows:
50 / 5x - y =
x=5
y=1
We and niece come up with 1, while the teacher marked the correct answer as -9. Can you help explain how she arrived at this answer?
Thanks for any help.
Rick
Hi Rick,
I find questions like this really annoying. It's like reading an English sentence that need a comma to make the meaning clear.
Students in school are sometimes taught a a rule called BEDMAS or PEDMAS. It indicates the order of operations in a mathematical expression.
- B(P) - brackets (parentheses)
- E - exponentiation
- D - division
- M - multiplication
- A - addition
- S - subtraction
If you follow this rule for your expression, there are no brackets or exponents so first you perform and divisions
50 / 5x - y = (50/5)x - y = 10x - y
Next the multiplication
10x - y= (10
5) - y = 50 - y
and then the subtraction
50 - y = 50 - 1 = 49
This procedure gives 50 / 5x - y = 49 when x=5 and y=1.
Your niece performed the multiplication first.
50 / 5x - y = 50 / (5x) - y = 50 / 25 - y
then the division
50 / 25 - y = 2 - y
and then the subtraction
2 - y = 2 - 1 = 1
This procedure gives 50 / 5x - y = 1 when x=5 and y=1.
I don't see how to get an answer of -9. I suppose you could perform the operations in the order
50 / (5x - y) = 50/(25-1) = 50/24 = 2.083
that is the multiplication, then subtraction and finally division but this doesn't give -9 either. I think there must be a typo somewhere.
I don't know any mathematician who would write 50/5x - y. We would all write it as
(50/5)x - y
or
50/(5x) - y
so that the meaning was clear.
Harley
Rick,
The answer of 1 appears correct to me as well. Perhaps there was a typo in the original question and y was supposed to be 11 and not 1, as this would yield an answer of -9.
Leeanne