Inequalities Drill Sheet

[dpulavarthi]

Problem 5
If a/b > c/d, which of the following must be true?
I. a/b - c/d > 0
II. ad < bc
III. ad > bc

A) I only
B) II only
C) III only
D) I and III only
E) I, II, and III

The answer is A.
How is III not true all the time? If a/b>c/d then cross multiply, ad>bc. Correct?

[vkakwani]

a=-2, b=-1, c=3,d=2

[suraj3185]

Here, we can not go for option 3 when sign is taken into picture.
if u take different signs for a and c .
Let a and b, c are positive and d is negtive
This indicates that ans is a

[tim]

thanks. let us know if there are any further questions on this one..

[dpulavarthi]

Got it ! thank you
Basically treat the a b c as variables and not as a solid equation.

[tim]

that's what it means when you see an a, b, or c in an equation.. :)