# Thread: Given a = c - d / 2ed, find a for c = 20, d = 10, e = 2

1. ## Given a = c - d / 2ed, find a for c = 20, d = 10, e = 2

This is driving me crazy:

Use the following formula to calculate a, if c = 20, d = 10 and e = 2:

. . . . .a = c – d/2e

2. Originally Posted by goldenmonkey
a = c – d/2e
Because there are no grouping symbols around the denominator, your typing means this:

$a = c - \dfrac{d}{2} \; \cdot \; e$

I'm thinking maybe you meant this, instead:

a = c - d/(2e)

These grouping symbols show that 2e is a denominator:

$a = c - \dfrac{d}{2e}$

It's important to type grouping symbols around numerators or denominators that contain more than one number or symbol. Otherwise, people can't be sure which way to go.

So, what happened, when you substituted the given values for the given symbols? Did you then try the arithmetic? For example, the equation c=20 tells us that we can replace symbol c with the number 20, anywhere we see it. That's called 'substitution'. Once you substitute all of the given values, do the arithmetic.

Need more help? Please show us what you tried (even if you think it's wrong).

Also, be sure to read the forum guidelines.

Here's a short video lesson.

3. ## Thank you

This was in an entrance exam to a diploma in financial planning, as far as I'm concerned the answer is 10. However that's not their take on it. Insisting the answer is 17.5. I understand that with the brackets that would change it but this is exactly how the equation was presented to me.

Use the following formula to calculate a, if c = 20, d = 10 and e = 2.
a = c – d/2e

4. Originally Posted by goldenmonkey
… as far as I'm concerned the answer is 10. However that's not their take on it. Insisting the answer is 17.5. I understand that with the brackets that would change it but this is exactly how the equation was presented to me.

Use the following formula to calculate a, if c = 20, d = 10 and e = 2.
a = c – d/2e
I agree with you. As presented, the answer is 10.

I parse the expression d/2e as d/2 · e because the Order of Operations tells us to do multiplication and division together in the order they occur, reading from left to right.

We do d/2 first, then we multiply that by e.

In order to obtain 17.5, there has to be a change to the Order of Operations. They made a mistake, by not printing grouping symbols to clearly indicate the denominator, that is, to force 2·e to be done before dividing d.

a = c - d/(2e) = 35/2 (or, 17.5 in decimal form)

5. I agree with you. As presented, the answer is 10.

I parse the expression d/2e as d/2 · e because the Order of Operations tells us to do multiplication and division together in the order they occur, reading from left to right.
Well I can sleep tonight.

Thank You.

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