So, this is how it goes: He did 4/10'ths of his wall, then he did 9/100'ths of his wall 4/10 9/100 you first need to find a least common denominator, which in this case would be 100, because 10*10=100, which is the lowest common denominator possible in this situation because 10*10=100, you have to multiply 4*10, which equals 40 now, you have 40/100 and 9/100 Add these together to get 49/100 It's already in lowest form, so no simplifying necessary The answer is C. 49/100
