15% of 16 equals 8% of what number?

Question

solve mentally

Answer 1

Henrik,
Yes, the key is to realize that 16 and 8 are related (twice as much).

The percent problem is:
   "15% of 16       is     8% of x"
    (15/100)*16    =     (8/100)*(x)
that also is:
    (15/100)*16    =     (x/100)*8
     "15%" of 16    is     x% of 8"
since 16 is twice 8:
    "15% of 16     is     30% of 8"
and (going in reverse again):
     (15/100)*16  =   (30/100)*8
     (15/100)*16  =    (8/100)*30
     "15% of 16    is     8% of 30"

 

This is a lot of lines of explanation, but, "in your head," it is mostly just switching numbers.

Answer 2

This is the percent problem.

The following equation is the key to solve this kind of problem.

Whole * n/100 = Part

The word "of" means multiplying and "is" means equal

In this case, there are two events: 15% of 16 and 8% of a number say x

We have the equation

15/100 * 16 = 8/100 * x

x = 0.15*16/0.08 = 30