book Maths Puzzle Numerical Ability

Not sure if this question is in the correct place, sorry if it is not.

The intensity level of an earthquake is based on the Richter scale. Using logarithms, the Richter scale me

Read Solution (Total 0)

book Other Question

the perimeter of a church window is 60 inches. if the window is in the shape of a regular pentagon, what is the length of each side of the window? Solve by Factoring:

x^2-9x=-20
x^2-9x+20=0
x^2-4x-5x+20=0
x(x-4)+(-5)(x-4)=0
(x-5)(x-4)=0
(x-5) or (x-4)
x=5 or x=4
Is this Correct? Thank you