21. which fractions are not equivalent?
à3/6=2/4
-b1/8=1/4
c1/3=2/6 d1/4=3/12

Explanation:

There are two ways to check to see if two fractions are equal.

Method 1) Cross multiplication

3/6 = 2/4

3*4 = 6*2

12 = 12

The last equation is true, so the first equation is true. This shows 3/6 and 2/4 are the same fraction

1/8 = 1/4

1*4 = 8*1

4 = 8

The last equation is false, so 1/8 = 1/4 is false. We found our answer.

1/3 = 2/6

1*6 = 3*2

6 = 6

This equation is true. So we can move on

1/4 = 3/12

1*12 = 4*3

12 = 12

A similar story happens with A and C.

Method 2) Comparing decimal forms

Using a calculator, we can find the decimal form of any fraction

3/6 = 0.5 and 2/4 = 0.5; since we get the same decimal value both times, this means 3/6 = 2/4 is a true statement. Choice A is ruled out.

1/8 = 0.125 and 1/4 = 0.25; we get different decimal values, so we can see that choice B is the answer

1/3 = 0.333 (the 3s go on forever) and 2/6 = 0.333... we have the same story as choice A, so we can rule out choice C.

1/4 = 0.25 and 3/12 = 0.25, same story as A and C. We can rule out choice D.

if you was gonna solve for a, a is a   < -12