Time and Work Questions

FACTS  AND  FORMULAE  FOR  TIME  AND  WORK  QUESTIONS

 

 

1. If A can do a piece of work in n days, then A's 1 day's work =1n

2. If A’s 1 day's work =1n, then A can finish the work in n days.

 

3. A is thrice as good a workman as B, then:

Ratio of work done by A and B = 3 : 1.

Ratio of times taken by A and B to finish a work = 1 : 3.

 

NOTE : 

Efficiency1No of time units

 

 Efficiency × Time = Constant Work

 

Hence, Required time = WorkEfficiency

 

Whole work is always considered as 1, in terms of fraction and 100% , in terms of percentage.

In general, number of day's or hours = 100Efficiency

Q:

A does 75% of a work in 25 days. He then calls in B and they together finish the remaining work in 5 days. How long B alone would take to do the whole work?

A) 50 days B) 80 days
C) 24 days D) 37.5 days
 
Answer & Explanation Answer: A) 50 days

Explanation:
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Q:

A is 50% more efficient than B. They together start the work and 7/12th of work is left after 8 days. Find in what time B alone will complete the whole work.

A) 36 days  B) 44 days 
C) 50 days  D) 40 days 
 
Answer & Explanation Answer:

Explanation:

Ratio of efficiency of A to B is 3 : 2

Let, In 8 days they complete = (3 + 2) × 8 = 40 units

So, total work = 40 × 12/5 units

Time taken by B alone to complete whole work = 40 ×  12/5 ×2 = 48 days 

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Q:

Application of Inverse Proportion

If 20 persons can do a piece of work in 7 days then calculate the number of persons require to complete the work in 28 days

Answer

Number of persons * days = work  


20 * 7 = 140 man- days 


 


Now,  x * 28  = 140 men- days


=> x =5         


Therefore in second case the required number of person is 5.


 


Second method:


Since work is constant, therefore  M1 x D1= M2 x D2


20 x 7 = M2 x 28


=> M2 = 5 


 

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Q:

P and Q were assigned to do a work for an amount of 1200. P alone can do it in 15 days while Q can do it in 12 days. With the help of R they finish the work in 6 days. Find the share of R ?

A) 120 B) 240
C) 360 D) 180
 
Answer & Explanation Answer: A) 120

Explanation:

1/15 + 1/12 + 1/R = 1/6, we got R = 60 (it means R will take 60 days to complete the work alone)


so ratio of work done by P:Q:R = 1/15 : 1/12 : 1/60 = 5 : 4 : 1


so R share = (1/10) x 1200 = 120.

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Q:

A laborer is engaged for 30 days on the condition that he receives Rs.25 for each day he works and is fined Rs.7.50 for each day is absent. He gets Rs.425 in all. For how many days was he absent ?

A) 10 days B) 14 days
C) 11 days D) 9 days
 
Answer & Explanation Answer: A) 10 days

Explanation:

For 30 days he receives

30 x 25 = 750
               

Actually he gets 425

Therefore, Fine is 750 - 425 =  325

 

=> No of days absent = 325/(25+7.50)= 10

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Q:

Sixty men can stitch 150 shirts in 30 days working 8 hours a day. In how many days can 35 men stitch 200 shirts working 6 hours a day ?

A) 87.5 B) 89
C) 91.5 D) 93.5
 
Answer & Explanation Answer: C) 91.5

Explanation:

We have M1 D1 H1 / W1 = M2 D2 H2 / W2 (Variation rule)
(60 x 30 x 8)/ 150 = (35 x D2 x 6) / 200
D2 = (60 x 30 x 8 x 200) / (150 x 35 x 6) => D2 = 91.42 days =~ 91.5 days.

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Q:

A take twice as much time as B or thrice as much time to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in ?

A) 3 hrs B) 6 hrs
C) 7 hrs D) 5 hrs
 
Answer & Explanation Answer: B) 6 hrs

Explanation:

Suppose A, B and C take x, x/2 and x/3 respectively to finish the work.
Then, (1/x + 2/x + 3/x) = 1/2
6/x = 1/2 => x = 12
So, B takes 6 hours to finish the work.

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Q:

A constructor estimates that 4 people can paint Mr. Karthik's house in 6 days. If he uses 5 people instead of 4, how long will they take to complete the job ?

A) 3 days B) 26/3 days
C) 13/4 days D) 24/5 days
 
Answer & Explanation Answer: D) 24/5 days

Explanation:

we know that m1 x d1 = m2 x d2
=> 4 x 6 = 5 x d
where d = no. of days taken by 5 men to paint
d = 24/5 days.

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