Problem Solving

At a certain diner, a hamburger and coleslaw cost $3.59, and a hamburger and french fries cost $4.40. If french fries cost twice as much as coleslaw, how much do french fries cost?

(A) $0.30
(B) $0.45
(C) $0.60
(D) $0.75
(E) $0.90

Yep. I've got the same thing:

Hamburger (H)
Coleslaw (C)
French fries (F)

Given:
H+C=3.59...(1)
H+F=4.40...(2)

Also, F=2C
Substitute the above in (2),
H+2C=4.40...(3)

Subtract (1) from (3)

We get: C=0.81
Thus, F=2C=2*0.81=$1.62=Wrong Answer choices in the original question

With keen observation you can eliminate the need of writing equations in such problems.

Clearly the difference in the price of the items purchased two at a time (with one common item) is 81 cents and one item being twice of the other implies the cost of the cheaper item itself is 81 cents. Hence the cost of french fries = 2*0.82=$1.62