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?

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