Multiple choice

A can do a piece of work in 30 days while B can do it in 40 days. In how many days can A and B working together do it?

  1. 70 days

  2. 171/4 days

  3. 190/7 days

  4. 120/7 days

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

A's rate = 1/30, B's rate = 1/40. Combined rate = 1/30 + 1/40 = (4+3)/120 = 7/120. Time = 120/7 days.

AI explanation

Using the Least Common Multiple (LCM) method, let the total work be 120 units. A's rate is 120 divided by 30, which is 4 units per day, and B's rate is 120 divided by 40, which is 3 units per day. Their combined rate is 7 units per day. Dividing the total work of 120 units by their combined rate gives 120/7 days.