Question

If P pencils cost D dollars, how many pencils can be bought for C cents?

I said d/p=100c/x
so x(d/p)=100c
x=100pc/d


but the answer is pc/100d
What did I do wrong?

Answer 1

Let me write the methodology to the answer then compare it to yours.
P pencils cost D dollars = D*100 cents
Thus one pencil costs 100d/p.
The number of pencils that can be bought by c cents will be
c/(100d/p) = pc/100d

Answer 2

perfect why do you multiply d by 100
100cent=1 dollar
100c=1d

Answer 3

I do that because c and d are unknowns. d may be 5 dollars.
To convert 5 dollars into cents, we multiply by 100, right?

Answer 4

I understand what you did but when I look at my work I can't see the mistake.
I know I did something wrong but what is it?

Answer 5

Your first statement is what made your working incorrect.
d/p=100c/x
Let's interpret it.
d/p gives is the price of a pencil in dollars, right?

Answer 6

yup

Answer 7

Good. Now, 100c is 100*(a certain number of cents) right?

Answer 8

yes to change cents to dollars

Answer 9

Remember, to get the number of dollars, we should divide by 100. not multiply. :)

Answer 10

ohhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh I kept thinking 100cents=1 dollar so you multiply

Answer 11

thanks I get stupid sometimes :D

Answer 12

Glad to be of help :)