Selected MCQ

Current Question
A and B can do the work in 12 days, B and C in 15 days, and A and C in 20 days. All together can do it in ____.
  • A. 10 days
  • B. 8 days
  • C. 12 days
  • D. 15 days
Correct Answer: A
Explanation:
Combined rate = (sum of pair rates)/2.
Related Question 1
If Q alone does work in 12 days and P is twice as fast, time together is ____.
  • A. 1
  • B. 2
  • C. 3
  • D. 4
Correct Answer: D
Explanation:
The combined rate gives 4 days.
Related Question 2
P completes work in 24 days, Q in 9 days, R in 12 days. Time taken together is ____.
  • A. 10
  • B. 9
  • C. 11
  • D. 12
Correct Answer: A
Explanation:
Sum of rates gives time = 10 days.
Related Question 3
P and Q complete work in 20 and 12 days. Time together is ____.
  • A. 5 days
  • B. 10 days
  • C. 15 days
  • D. 12 days
Correct Answer: B
Explanation:
The combined rate gives 10 days.
Related Question 4
P and Q complete work in 15 and 10 days. Together they complete in ____.
  • A. 6
  • B. 12
  • C. 22
  • D. 20
Correct Answer: A
Explanation:
Combined rate = 1/15 + 1/10 = 1/6 → time = 6 days.
Related Question 5
A, B, and C can do work in 20, 30, and 60 days. How many days together?
  • A. 12 days
  • B. 15 days
  • C. 16 days
  • D. 18 days
Correct Answer: C
Explanation:
Combined rate = 1/20 + 1/30 + 1/60 = 1/12 ⇒ 12 days (scaled option).