Three men finish painting a wall in 8 days. Four boys do the same job in 7…
2023
Three men finish painting a wall in 8 days. Four boys do the same job in 7 days. In how many days will 2 men and 2 boys working together paint two such walls of the same size ?
- A.
11 12/11 days
- B.
12 12/13 days
- C.
16 days
- D.
12 days
Attempted by 6 students.
Show answer & explanation
Correct answer: B
Key facts: three men finish one wall in 8 days and four boys finish one wall in 7 days.
One man's one-day work = 1/(3×8) = 1/24.
One boy's one-day work = 1/(4×7) = 1/28.
Two men and two boys' combined one-day work = 2×(1/24) + 2×(1/28) = 13/84.
Time to paint one wall = 1 ÷ (13/84) = 84/13 days. For two walls: 2×(84/13) = 168/13 = 12 12/13 days.
Answer: 168/13 = 12 12/13 days.