Question

A can do a piece of work in 4 hours and B can do it in 6 hours. How much time would they take working together to finish the work?

Answer 1

5 hours

Explanation:

A = 4hours

B= 6 hours

Average of A and B = (4hours+6hours)/2 = 5hours

Answer 2

2.4 hours

Explanation:

Let total work = X

Rate of work done = X ÷ time

Rate of A = X/4

Rate of B = X/6

If they work together, rate is the sum of their individual rates, i.e.

X/4 + X/6

= (3X + 2X)/12 (taking LCM)

=5X/12

Rate = X/time

5X/12 = X/time

time = X÷(5X/12)

time = X × 12/(5X)

time = 2.4 hours

Shortcut:

Product of individual times/sum of individual times

= (4×6)/(4+6)

=24/10

=2.4 hours