Problem Solving

A paint crew gets a rush order to paint 80 houses in a new development. They paint the first y houses at a rate of x houses per week. Realizing that they'll be late at this rate, they bring in some more painters and paint the rest of the houses at the rate of 1.25x houses per week. The total time it takes them to paint all the houses under this scenario is what fraction of the time it would have taken if they had painted all the houses at their original rate of x houses per week?

(A) 0.8(80 – y)

(B) 0.8 + 0.0025y

(C) 80/y – 1.25

(D) 80/1.25y

(E) 80 – 0.25y

Please explain, thank
no OA
Source: Manhattan challenge problem

Answer is B

Total time taken with the original scheme = y/x + (80-y)/1.25x --- (1)

Total time taken if they had gone ahead with xhouses/week scheme = 80/x ---- (2)

Question is asking for ratio of (1) and (2).. so just solve (1)/(2)

you will get (1)/(2) = 0.8 + 0.0025y