Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
If 15 men can build a wall in 20 days, how many men are required to build the same wall in 12 days?
20
25
30
18
25
Use the Inverse Proportion logic: since the number of days decreases from 20 to 12 (ratio 5:3), the number of men must increase by the reciprocal ratio (3:5). Thus, 15├Ч(5/3)=25.
15 men can build a wall in 20 days. We need to find the number of men required to build the same wall in 12 days.
M1тАЛ├ЧD1тАЛ=M2тАЛ├ЧD2тАЛ
Use the Inverse Proportion logic: since the number of days decreases from 20 to 12 (ratio 5:3), the number of men must increase by the reciprocal ratio (3:5). Thus, 15├Ч(5/3)=25.
Students often wrongly apply direct proportion, calculating 15├Ч(12/20)=9, forgetting that fewer days require more workers (inverse variation).
Identify given variables
Set the initial number of men M1тАЛ=15 and initial days D1тАЛ=20. The target days D2тАЛ=12.
M1тАЛ=15,D1тАЛ=20,D2тАЛ=12
Apply the Work formula
Since the work (building one wall) is constant, we use the inverse relationship between men and days: M1тАЛD1тАЛ=M2тАЛD2тАЛ.
15├Ч20=M2тАЛ├Ч12
Calculate the unknown variable
Solve for M2тАЛ by dividing the product of initial values by the target days.
M2тАЛ=1215├Ч20тАЛ=12300тАЛ=25
B is correct because the calculation M2тАЛ=25 confirms that 25 men are needed to complete the task in 12 days.
This inverse variation principle is identical to the pipe and cistern problems where flow rate and time are inversely proportional.
Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.
Free Download тАв 100K+ Aspirants