Question

A mathematics book has 360 pages, of which 50% are on ALgebra, 20% on Geometry and the remainder on Arithmetic. How many pages of arithmetic are there in the book?
Damon
50 % + 20% = 70%
then
100% - 70% = 30%
so
0.30 * 360
Sparrow
A mathematics book has 360 pages, of which 50% are on ALgebra, 20% on Geometry and the remainder on Arithmetic. How many pages of arithmetic are there in the book?

I'm seeing that the answer is 108 pages but I can't understand how to arrive at that answer.
PsyDAG
Look at what Damon did.

.3 * 360 = ?