Time and Work | Maths

• If A can do a piece of work in `n' days,then A's 1 day work is 1/n
• If M1 persons can do W1 work in D1 days for T1 hours and M2 persons can do W2 work in D2 days for T2 hours then

M1 D1 T1 W2 = M2 D2 T2 W1

• If A can finish a work in `x' days and B can finish the same work in `y' days, then time taken by both to finish the work is xy / (x+y) days.

[Here 1 day work A=1/x , B=1/y .

So 1 day both A+B work= 1/x + 1/y =(x +y) /xy .

Number of days = xy / (x+y) ]

• If A and B together can do a piece of work in x days and A alone can do it in y days then B alone can do it in xy/ (y-x) days
• If A, B and C can do a work in x,y, and z days respectively, then all of them working together can finish the work in xyz / (xy +yz + xz) days

Questions

1.If 18 members can complete a work in 12 days. How may more members are needed to complete this work in 9 days? (Fireman Driver NCA 2020)

M1 D1=M2 D2

18 x 12= M2 x 9

M2=18*12/9 = 24

More members 24-18=6

2.A and B together can finish a work in 20 days. If A alone can complete the same work in 12 days, in how may days can B alone complete that work?
(Fireman Driver NCA 2020)
xy/ (y-x)
20*12/(20-12)
20*12/8
30

2018
1.If 18 persons can do a work in 28 days, how many persons are needed to complete the same work in 24 days. (Caretaker Male 2018)

M1 D1=M2 D2

18 x 28= M2 x 24

M2=18*28/24 = 21

2.15 members can complete a work in 12 days. How many more members are needed to complete this work in 9 days ? (Women Civil Excise Officer 2018)

M1 D1=M2 D2

15 x 12 = M2 x 9

M2 = 15x 12/9 = 20

More members 20-15=5

3.A can finish a work in 20 days. A and B together can finish the work in 12 days. Then B alone can finish the work in
(Beat Forest Officer 2018)
xy/ (y-x)
20*12/(20-12)
20*12/8
30

4.4 പേർ ചേർന്ന് 9 ദിവസം കൊണ്ട് തീർക്കുന്ന ഒരു ജോലി 6 ദിവസം കൊണ്ട് തീർക്കണമെങ്കിൽ എത്ര ജോലിക്കാരെ കൂടി കൂടുതലായി വേണ്ടിവരും?
(WOMEN POLICE CONSTABLE NCA 2018)
M1 D1=M2 D2
4 x 9=M2 x 6
M2 =6
ജോലിക്കാർ കൂടുതലായി വേണ്ടി വന്നതു = 6-4 =2

5.400 തൊഴിലാളികൾക്ക് 75 ദിവസം കൊണ്ട് ഒരു ജോലി പൂർത്തിയാക്കാൻ കഴിയും. അതിൽ നിന്ന് 25 തൊഴിലാളികളെ മാറ്റിയാൽ ആ ജോലി പൂർത്തിയാക്കാൻ എത്ര ദിവസം വേണ്ടിവരും? 
(Security Guard- Government Secretariat 2018)
M1 D1=M2 D2
400 x 75=375 x D2
D2=80

6.Janaki and Janu can do a piece of work in 8 days. Janaki alone can do it in 12 days. How long would Janu take to do the same work ?
(Civil Police Officer 2018)
xy/ (y-x)
8*12/(12-8)
8*12/4
24


7.40 men can do a piece of work in 20 days. If there are 50 men to do the same work how long will they take to finish it ?
(Sergeant 2018)
M1 D1=M2 D2
40 x 20=50 x D2
D2=16 days

2017
1.If 30 men working 8 hrs. a day can do a piece of work in 16 days in how many days will 24 men working 5 hrs. a day will do the same piece of work.
(ARMED POLICE SUB INSPECTOR TRAINEE 2017)
M1 T1 D1 = M2 T2 D2
30 x 8 x 16 = 24 x 5 x D2
D2= 2*16 = 32

Previous
Next