Chain Rule Practice Questions

5 questions per page • Detailed step-by-step solutions

Question 1
Easy
If 8 men can reap 40 hectares in 12 days, then how many hectares can 30 men reap in 20 days?
A 220 hectares
B 240 hectares
C 250 hectares
D 280 hectares
Correct Answer: C

Explanation:

Using (M1 * D1) / W1 = (M2 * D2) / W2: (8 * 12) / 40 = (30 * 20) / W2 => 96 / 40 = 600 / W2 => 2.4 = 600 / W2 => W2 = 250 hectares.
Question 2
Easy
A rope makes 70 rounds of the circumference of a cylinder whose radius of the base is 14 cm. How many times can it go round a cylinder with radius 20 cm?
A 45 times
B 49 times
C 52 times
D 56 times
Correct Answer: B

Explanation:

Total length of rope = 70 * (2 * pi * 14). Let N be rounds for radius 20 cm: N * (2 * pi * 20) = 70 * (2 * pi * 14) => 20 * N = 70 * 14 => N = 980 / 20 = 49 times.
Question 3
Easy
4 persons can prepare an admission list in 8 days, working 7 hours a day. If 3 persons join them so as to complete the work in 4 days, how many hours per day must they work?
A 6 hours
B 7 hours
C 8 hours
D 9 hours
Correct Answer: C

Explanation:

New workers = 4 + 3 = 7. M1 * D1 * H1 = M2 * D2 * H2 => 4 * 8 * 7 = 7 * 4 * H2 => 224 = 28 * H2 => H2 = 8 hours/day.
Question 4
Easy
A garrison of 500 men had provision for 27 days. After 3 days a reinforcement of 300 men arrived. For how many more days will the remaining food last now?
A 12 days
B 15 days
C 16 days
D 18 days
Correct Answer: B

Explanation:

After 3 days, remaining food is sufficient for 500 men for (27 - 3) = 24 days. Total men now = 500 + 300 = 800 men. By chain rule (M1 * D1 = M2 * D2): 500 * 24 = 800 * D2 => D2 = (500 * 24) / 800 = 15 days.
Question 5
Easy
If 7 maids with 7 mops cleaned 7 floors in 7 hours, how long would it take 3 maids to mop 3 floors with 3 mops?
A 3 hours
B 7 hours
C 14 hours
D 21 hours
Correct Answer: B

Explanation:

Using (M1 * T1) / W1 = (M2 * T2) / W2: (7 * 7) / 7 = (3 * T2) / 3 => 7 = T2. Hence, 3 maids take 7 hours.