Each input should only have 1 output. Multiple inputs can have the same output, but one input can only correspond to a single output.
Also, if you graph the relation with the input as the x coordinate and output as the y coordinate, you can then conduct a verical line test. Anywhere you draw a vertical line, you should only intersect the curve one time.
Hack way
25%=1/4
13 is 1/4 of something
1/4 times 4=4/4=1
therefor
13 times 4=1 whole
13*4=52
the original number is 52
Assume independence because there are probably a lot of widgets. 1/100 x 1/100 = 1/10,000
3-4: Definition of supplementary angles
5: Simplify
