Question

Mary reduced the size of a painting to a width of 3.3 in. What is the new height if it was originally 32.5 in tall and 42.9 in wide?

Answer 1

The ratio of the height and width remain constant as you change it's size.
So..
A = Old width
B = Old height
C = New width
D = New height

A/B = C/D

Plug in the values we have

42.9 / 32.5  = 3.3 / D

Multiple both sides by D
D * 42.9 / 32.5 = 3.3

Multiple both sides by 32.5

D * 42.9 = 3.3 * 32.5

Now divide both sides by 42.9

D = 3.3 * 32.5 / 42.9

Now simply do the multiplication and division using the available numbers.
D = 2.5