I had the same setup equation, but that quadratic equation is BRUTAL.
yup thats why i posted the question.. to see if anyone else had another approach to avoid quadratic eqn
so far nil..
You could work backward from the answer choices. Start with C:
Suppose A takes 20 minutes for 80 pages. Then A's rate is 4 pages per minute, or 40 pages in 10 minutes. B's rate is 40 pages in 6 minutes, or 40/6. Combined, their rates are 4 + (40/6) = 64/6, which is greater than 50/6. So the rate for A yielded by this answer choice is too high. A must take more than 20 minutes to print 80 pages.
So move on to D. A's rate is 80/24 or 10/3 pages per minute. A takes 12 minutes for 40 pages, so B takes 8, and B's rate is 40/8 = 5. Their combined rate is 10/3 + 5 = 10/3 + 15/3 = 25/3 = 50/6. There's the answer.