Instructions: DO NOT USE CALCULATOR. Figures are not drawn to scale. Arif can do a work in 12 hours. Arif finished two-thirds of the work and the remaining portion of the work was done by Babu, whose rate of working is just 20% of what Arif can do. How long did it take Babu to finish the remaining work in hours?
A. 8
B. 20
C. 24
D. 32
E. none of these
Explanation: (B) Arif's rate (\(R_A\)): \(\frac{1}{12}\) of the work per hour. Work remaining = \(1 - \frac{2}{3} = \frac{1}{3}\). Babu's rate (\(R_B\)): 20% of Arif's rate = \(0.20 \cdot R_A = \frac{1}{5} \cdot \frac{1}{12} = \frac{1}{60}\) of the work per hour. Time for Babu to finish the remaining \(\frac{1}{3}\) work: \(T_B = \frac{\text{Work}}{\text{Rate}_B} = \frac{1/3}{1/60} = \frac{1}{3} \cdot 60 = 20 \text{ hours}\).
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