Let A, B and C be the hours needed for each friend to paint the house on his own and D the number of hours needed if they paint all together.

Then

A = D+1

B = D+5

C = D+8

In one hour, Alan has painted 1/A of the house, Brian 1/B and Chester 1/C, so all together have painted 1/A+1/B+1/C.

Thus in D hours they have painted D*(1/A+1/B+1/C) and we have:

D*(1/A+1/B+1/C)=1 (the entire house).

By substituting A, B and C from the above equations, we finally get:

D^3 + 7D^2-20=0. We keep the only acceptable solution D=1,531129 (the other two are negative).

So we have: A=2,531129 B=6,531129

Now that A and B will paint the house:

Let X be the number of hours we are looking for.

Χ*(1/A+1/B)=1. By substituting the above values of A and B, we get X = 1,824173, which is what you got, guys!

Thanks!!