If the ratio of the rise to run on the pitch of a roof is 7/10 and the run is 30 feet, what is the rise?

Answer 1

This is one you can just think through verbally - for each 10 feet of run (horizontal), the rise (height) of the roof changes by 7 feet.

Over 30 feet, which can be thought of as "3 runs of 10", the rise (height) will change by "3 rises of 7", or 21.

Or, (7/10) x 30 = 21 feet.