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Question
Joseph and Peter can complete a work in 20 hours and 25 hours respectively. Find :
(i) work done by both together in 4 hrs.
(ii) work left after both worked together for 4 hrs.
(iii) time taken by Peter to complete the remaining work.
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Solution
Joseph can do a work in = 20 hours
Peter can do the same work in = 25 hours
Now Joseph's 1 hour's work = `1/20`
and Peter's 1 hour's work = `1/25`
Both's 1 hour's work = `1/20 + 1/25 = (5 + 4)/100 = 9/100`
(i) Both's 4 hours work `= 9/100 xx 4 = 9/25`
(ii) Work left over `= 1 - 9/25`
`= (25 - 9)/25 = 16/25`
(iii) Peter can do `16/25` work in `= 25 xx 16/25` = 16 hours
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