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Unitary Method (Including Time and Work) — MATHS STD 7 — Question

ICSE BoardEnglish MediumSTD 7MATHSUnitary Method (Including Time and Work)4 Marks
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.
✓

Answer

Joseph can do a work in $=20$ hours
Peter can do the same work in $=25$ hours
Now Joseph's 1 hour's work $=\frac{1}{20}$
and Peter's 1 hour's work $=\frac{1}{25}$
Both's 1 hour's work $=\frac{1}{20}+\frac{1}{25}=\frac{5+4}{100}=\frac{9}{100}$
(i) Both's 4 hours work $=\frac{9}{100} \times 4=\frac{9}{25}$
(ii) Work left over $=1-\frac{9}{25}$
$ =\frac{25-9}{25}=\frac{16}{25} $
(iii) Peter can do $\frac{16}{25}$ work in $=25 \times \frac{16}{25}=16$ hours

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