Time and Work - Arithmetic Aptitude Questions and Answers

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A can complete a wall in 30 hours. B uses 30 bricks per hour, and together they can finish the wall in 12 hours. How many bricks are in the wall?

800 bricks

600 bricks

620 bricks

500 bricks

Answer : Option B

Explanation :

Note: Assume the total work = LCM of the given time

Take the LCM of hours = LCM of (30 and 12) = 60
Let the total work = 60

Note: One hour work = (total work/ time)

A's one hour work = 60/30 = 2 unit
(A+B)'s one hour work = 60/12 = 5 unit
B's one hour work = 2+B = 5 units, or, B = 3 units

B alone can complete the work in 60/3 = 20 hours
And, B uses 30 bricks per hour.