Question

12 is 30% of ____ (Please explain)

Answer 1

Answer:

40

Step-by-step explanation:

In word problems, the word "of" usually means multiply.  Thus, for example, 10% of $50 is $5.  This is because we can write 10% as 0.10 or as 10/100 (which is 1/10) and then multiply:    (1/10)(50) = 5

So, we often see equations like:

    R = (1/2)D        meaning R is 50% of D, or R is half of D

Let x = the number we want to find

This problem says:

 "12 is 30%       of    what number?"

  12 = (30/100) *        x

12 = (3/10)x

(10/3)12 = x             [multiply both sides by (10/3)]

    40 = x        

Checking (very important):      

 Is   12 = (3/10)(40)    ?

       12 = (3)(4)    ?

       12 = 12     ? yes

Answer 2

Answer:

40

Step-by-step explanation:

Let x = unknown number

30% = 30/100 = 0.3

If 12 is 30% of x, then

   30% of x is 12

⇒ 0.3x = 12

⇒ x = 12 ÷ 0.3

⇒ x = 40

Or, you can divide 12 by 3 to get 10% and then multiply this by 10 to get 100%:

12 ÷ 3 = 4 (so 4 is 10%)

4 × 10 = 40 (which is 100%)