Guide 3, Chapter 13, pg. 195, Question 6

[tex.boonjue]

if a, b, and c are greater than 0 and a is twice as large as b percent of c, then in terms of b and c, what is a percent of c?

*the book shows how to solve this question using the pick numbers and calculate a target approach, but I want to see how it is done algebraically.

This is what I did.

(b/100)c = 2a => (bc/100) = 2a

a= (bc)/(200)

(a/100)c = (ac/100)

plug in for "a" and you get the following.

(bc^2)/(2000)

Which is NOT the correct answer.

The correct answer is (bc^2)/(5000)



PLEASE someone explain this to me, it is incredibly frustrating.

[LazyNK]

Note that a=2*b*c/100 and not 2*a=b*c/100 as you have used.
-NK

[jnelson0612]

Note that a=2*b*c/100 and not 2*a=b*c/100 as you have used.
-NK

Excellent! And I think this is a wonderful illustration of why most of us should not even bother with algebra. Picking numbers is fast, simple, and foolproof.