Question

semicircle R ~ semicircle S
r/s=3/5
Area of semicircle S = 75π cm2
Area of semicircle R = ?

Answer 1

The formula for the area of a circle is \[\pi r^2\]
So in other words, the area depends on radius-squared
Assuming the two semicircles are similar fractions of the total circle, the ratio between the two areas should be the ratio between the radii squared:

So AreaR/AreaS = (r/s)^2
AreaR/75pi = (3/5)^2
AreaR = 75pi * 9/25
AreaR = 27pi