39 people can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work? - Sri Chaitanya Infinity Learn Best Online Courses for NCERT Solutions, CBSE, ICSE, JEE, NEET, Olympiad and Class 6 to 12

A
$13$
B
$14$
C
$15$
D
$10$

Solution:

Concept- Time and work share a fundamental idea in common with other arithmetic topics, namely the idea of proportionality. When the amount of work is constant, efficiency is inversely proportional to the length of time required.
Finding the required time for 30 persons, working 6 hours a day by unitary method.
Given as we know,
39 people can repair a road in 12 days, working 5 hours a days suppose the whole work is 1
Now,
39 people in 12 days by working 5 hours in a day

= \frac{1}{39}

Hence,
One person in a day by working 1 hour

= \frac{1}{39} x 12 x 15 .

Now,
Suppose 39 person done their in x days

= \frac{1}{30 \times x \times 6}

= \frac{1}{30 \times x \times 6} = \frac{1}{39 \times 12 \times 5}

= 30 \times x \times 6 = 39 \times 12 \times 5

x = \frac{39 \times 12 \times 5}{30 \times 6}

x = \frac{39 \times 2}{6} = 13 days

Hence, the correct option is 1) 13 days.

Solution:

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