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If 10 men can build a wall in 20 days, how long will 20 men take to build the same wall?
10 days
15 days
5 days
20 days
10 days
Since the number of men is doubled, the time required is halved in inverse proportion (20/2=10 days).
Initial men M1тАЛ=10, Initial days D1тАЛ=20, Final men M2тАЛ=20
M1тАЛ├ЧD1тАЛ=M2тАЛ├ЧD2тАЛ
Since the number of men is doubled, the time required is halved in inverse proportion (20/2=10 days).
Multiplying the values instead of using the inverse proportion rule for work and time.
Identify Given Data
Note the initial number of workers and the days they take to complete the work: M1тАЛ=10 men, D1тАЛ=20 days.
M1тАЛ=10,D1тАЛ=20
Calculate Total Man-Days
The total amount of work required is measured in man-days, which is the product of men and days: W=M1тАЛ├ЧD1тАЛ=10├Ч20=200 man-days.
W=10├Ч20=200
Apply Formula for New Workforce
Divide the total man-days by the new number of men (M2тАЛ=20) to find the new duration (D2тАЛ): D2тАЛ=M2тАЛWтАЛ=20200тАЛ=10 days.
D2тАЛ=20200тАЛ=10
A is correct because doubling the number of men halves the time required, resulting in 10 days.
Understanding inverse proportion helps solve speed-time and pipe-cistern problems efficiently.
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