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X, Y and Z together can do a piece of work in 16 (4/11) days. X and Y together can do the same work in 20 days. In how many days will Z alone finish the 60% of the work?

Solution

✅ Correct Option: 2

X, Y and Z together finish work in 16 (4/11) days.

Converting to improper fraction:

16411=16×11+41116 \dfrac{4}{11} = \dfrac{16 \times 11 + 4}{11}

=176+411= \dfrac{176 + 4}{11}

=18011= \dfrac{180}{11} days


Work rate of (X + Y + Z) together:

Work rate =1time taken=1180/11=11180= \dfrac{1}{\text{time taken}} = \dfrac{1}{180/11} = \dfrac{11}{180} work per day


X and Y together take 20 days.

Work rate of (X + Y) together:

Work rate =120= \dfrac{1}{20} work per day


Z's work rate alone is the difference between the combined rate and (X + Y)'s rate:

Z's work rate =11180−120= \dfrac{11}{180} - \dfrac{1}{20}

=11180−9180= \dfrac{11}{180} - \dfrac{9}{180}

=2180= \dfrac{2}{180}

=190= \dfrac{1}{90} work per day


Z completes the full work in:

Time =11/90=90= \dfrac{1}{1/90} = 90 days


For 60% of the work:

Time =90×0.6= 90 \times 0.6

=54= 54 days

Therefore, Z alone will finish 60% of the work in 54 days.

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