Let’s focus on arithmetic QnA

Hyderabad: Let’s calculate the amount of time you take to solve these problems This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exam. Here are some previous year questions and explanations on the Time and Work topic. To improve calculations speed, the aspirants must practice questions from the previous question papers.

1) A person A taken 7 1/2 days to finish 5th/8 of a work then the number of days required for A to finish the complete work is (SI MAINS 2018)

A. 9 B.12 C. 15 D. 18

Ans: B

Explanation:

Time required to complete the total work is = (15⁄2)/(5⁄8) = 12

=>; A can complete the work in 12 days

2) A person P can complete a work in 40 days. A second person Q can complete the same work in 35 days. Both P and Q work together for 14 days and then P goes away. The number of days that Q taken to complete the remaining work is (SI MAINS 2018)

A. 12 1/4 B. 10 1/2 C. 9 3/4 D. 8 3/4

Ans: D

Explanation:

Let total work be 280 units. ( LCM of 40,35)

Hence, P completes 7 units/day and Q completes 8 units/day

Total work done per day working together = 15 units

Total work done in 14 days together = 15× 14 = 210 units

Remaining work = 280-210 = 70 units

Time taken by Q to complete the remaining work = 70/8 = 8 3/4

3. Twenty men complete a work in 16 days. Twenty women complete the same work in 18 days. If all these men and women work together, then the number of days required to complete that work

(SI MAINS 2018)

A. 10 1/3 B. 9 8/17 C. 9 1/15 D. 8 8/17

Ans: D

Explanation:

20 men do a work in 16 days

20 men do 1/16 part of work in one day

20 women do 1/18 part of work in one day

Together they do 1/16 1/18 = 17/144 part in one day

Together the work is completed in 144/17 days= 8 8/17 days

4. A person A can complete a work in 15 days working 8 hours daily. A second person B can complete the same work in 20 days working 7 hours a day. If both A and B work together, working 7 hours a day, then the number of days required to complete that work is (SI MAINS 2018)

A. 8 5/13 B. 9 3/(13 ) C. 9 6/13 D. 10 1/4

Ans: B

Explanation:

Time taken by A = 15 × 8 = 120 hours

Time taken by A = 20 × 7= 140 hours

Total work = LCM of (120, 140) = 840 units

So A can complete 7 units and B can complete 6 units per hour

Together they can complete 13 units per hour

No. of units completed in a day = 13*7 = 91

No. of days required to complete the work = 840/91 = 9 3/(13 ) days

5. Two persons A and B can do a work in 24 and 30 days respectively. After working together for some days, A left. B finished the remaining work in 12 days. Then, the number of days that A worked is (SI MAINS 2018)

A. 8 B. 9 C. 10 D. 11

Ans: A

Explanation:

Let A work for x days with B

B = (x 12) days

x/24 (x 12)/30 = 1

5x 4x 48 =120

9x = 72

x = 8 days

-Banda Ravipal Reddy

Director, SIGMA

Sai Institute of General Mental Ability

Hyderabad