Question: If 5 workers can paint a house in 8 hours, how long would it take 20 workers to paint the same house?

Solution:
 5 workers can paint a house in 8 hours
∴ 1 worker would take = (8 × 5) hours
∴ 20 workers would take = (8 × 5)/20 hours
= 2 hours

Question: A takes three times as much time as B or twice as much time as C to finish a piece of work. Working together, they can finish the work in 3 days. B can do the work alone in how many days?

Solution:
ধরা যাক,
A, B ও C যথাক্রমে কাজটি শেষ করতে সময় লাগে x, x/3, এবং x/2 দিন।

তারা একসাথে ৩ দিনে কাজ শেষ করে।
অর্থাৎ তাদের একদিনের কাজ হলো 1/3।

∴ A + B + C এর একদিনের কাজ = (1/x) + (3/x) + (2/x)
= (1 + 3 + 2)/x
= 6/x

এখন,
6/x = 1/3
∴ x = 18

∴ B একা কাজ শেষ করতে সময় নেবে = 18/3 = 6 দিন।

Question: A man completes 2/5 of a work in 8 days. If his work rate is doubled, how many more days will it take him to finish the remaining work?

Solution:
2/5 of the work is done in = 8 days
∴ full work is done in = (8 × 5)/2 days
= 20 days

∴ His daily work rate = 1/20 per day

If his work rate is doubled, his new daily work rate is,
= (1/20) × 2 = 1/10 per day

Remaining portion of the job = 1 - (2/5)
= 3/5

Now,
1/10 work is done in = 1 day
∴ 3/5 work is done in = (3/5) ÷ (1/10) days
= (3/5) × 10
 = 6 days

Therefore, it will take him 6 more days to finish the job.