Multiple choice

A, B and C can complete the work in 10 days, 30 days and 15 days respectively. If A and B together is helped on every 2nd day by C, in how many days the work will be completed?

  1. 4 days

  2. 6 days

  3. 7 days

  4. 8 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A's rate = 1/10, B's rate = 1/30, C's rate = 1/15. Day 1: A+B work = 1/10 + 1/30 = 4/30 = 2/15. Day 2: A+B+C work = 2/15 + 1/15 = 3/15 = 1/5. In 2 days, they complete 2/15 + 3/15 = 5/15 = 1/3 of the work. In 6 days, they complete 3 * (1/3) = 1 full work.

AI explanation

Using the LCM method, let the total work be 30 units, making the daily work rates of A, B, and C equal to 3, 1, and 2 units respectively. A and B work every day to complete 4 units, and on every second day C helps them to complete an additional 2 units, meaning they complete 4 + 4 + 2 = 10 units over every two-day cycle. Completing 30 units requires exactly 3 such cycles, totaling 6 days of work.

Keep practicing — related questions