I spend 20 hours cleaning my garden. How long will it take if 4 people (with the same efficiency) come to join me?

A) 3 hours

B) 6 hours

C) 5 hours

D) 4 hours

I compete the task in = 20 hours

4 people join with the same efficiency

So,

The total persons working now

= (Me + 4 people)

= (1+4)

= 5

Now,

1 people can finish in = 20 hours

5 people can finish in = 20/5 = 4 hours

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