Multiple choice

A works twice as fast as B and B works twice as fast as C. All three working together can finish a task in 4 days with the help of D. If D alone can finish the same task in 16 days, then in how many days will A alone finish 75% of the same task?

  1. 8

  2. 7

  3. 9

  4. 6

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let C = x, B = 2x, A = 4x. Combined rate = 7x. (7x + 1/16) * 4 = 1. 28x + 1/4 = 1 => 28x = 3/4 => x = 3/112. A's rate = 4x = 12/112 = 3/28. Time for 75% work = (0.75) / (3/28) = (3/4) * (28/3) = 7 days.