CBSE Mathematics Class VIII (8th) MCQ Time and Work
CBSE Mathematics
Class VIII (8th) MCQ Time and Work
A alone can do a
piece of work in 6 days and B alone can do it in 12 days. In how many days will
A and B together do the same work?
a.
2 days b. 3 days c. 4 days d. 5 days
Time taken by A to finish the work = 6 days
Time taken by B to finish the work = 12 days
Work done by A in 1 day = 1/6
Work done by B in 1 day = 1/12
Work done by (A + B) in 1 day = ( 1/6 + 1/12 ) = 3/12 = 1/4
Time taken by (A+ B) to finish the work = 4 days.
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Rohit can finish a
work in 30 days. Rohit and his friend Rohan working together can finish it in
12 days. In how many days can Rohan do it alone?
a.
15 days
b. 20 days c. 25 days d. 30 days
Answer:
Time taken by ( Rohit + Rohan) to finish the work = 1 2 days
Time taken by Rohit alone to finish the work = 30 days
(Rohit + Rohan)’s 1 day’s work = 1/12
Rohit’s 1 day’s work = 1/30
Rohan’s 1 day’s work = {(Rohit + Rohan)’s 1 day’s work -
Rohit’s 1 day’s work}
=(1/12 – 1/30 ) = 3/60 =
1/20
Hence, Rohan alone can finish the work in 20 days.
John do a piece of
work in 16 days and Jenny can do the same work in 12 days. But John, Jenny and
Dick do the work in 6 days. So, in how many days Dick alone can do the work?
a.34 days
b. 22 days c. 36
days d. 48 days
Answer:
John do the work in 16 days
Jenny do the work in 12 days.
(John + Jenny + Dick) do the work in 6 days
John’s 1 day’s work = 1/16
Jenny’s 1 day’s work = 1/12
( John + Jenny + Dick)’s 1 day’s work = 1/6
(John + Jenny)’s 1 day’s work = ( 1/16 + 1/12 )= 7/48
Hence, Dick’s 1 day’s work = { ( John + Jenny + Dick)’s 1
day’s work - (John + Jenny)’s 1 day’s work }
= (1/6 – 7/48 ) = 1/48
Dick do the work in 48 days.
If Ritam take 50%
more time than Rohan to do a work and if they together do the work in 18 days
then find how much time shall Ritam take to do the work?
a.30 days b. 35 days c. 40 days d. 45 days
Answer:
Let, Rohan do the work in x days.
Therefore, Ritam do the work in (150x/100) = (3x/2) days
Rohan’s 1 day’s work = 1/x
Ritam’s 1 day’s work = 2/3x
(Rohan + Ritam)’s 1 day’s work = (1/x + 2/3x)= 5/3x
But ( Rohan + Ritam)’s 1 day’s work = 1/18
By condition,
5/3x = 1/18
X = 30
Therefore, Ritam do the work = (3*30)/2 = 45 days
Priyojit works twice
as fast as Pritam. If together they finished the work in 12 days, then how much
time Pritam take to do the work?
a.24 days
b. 27 days c. 36
days d. 48 days
Answer:
Let, Pritam’s 1 day’s work = x
Therefore, Priyojit’s 1 day’s work = 2x
( Pritam + Priyojit)’s 1 day’s work = (x+2x)
But, ( Pritam + Priyojit) do the work in 12 days
Therefore, ( Pritam + Priyojit)’s 1 day’s work = 1/12
By condition,
X+2x = 1/12
X = 1/6
Pritam finish the
work in 36 days.
Snehesh do a work in
10 days and Suvam in 15 days. If they work together and finish the work; then
out of total wages of Rs 3000, how much money Snehesh get?
a.
Rs 1200 b. Rs 1500 c. Rs 1800 d. Rs 2000
Answer:
Snehesh finish the work in 10 days
Suvam finish the work in 15 days
Snehesh do work in 1 day = 1/10
Suvam do work in 1 day = 1/15
Therefore, ratio of the wages of Snehesh and Suvam = 1/10 :
1/15 = 3:2
Snehesh will get = (3*3000)/5 = Rs 1800
Rock and Tom together
can do a piece of work in 12 days; Tom and John together can do it in 20 days
and John and Rock can do it in 15 days. How much time takes to finish the work
if they work together?
a.
6 days
b. 9 days c. 10 days d. 11 days
Answer:
Time taken by ( Rock + Tom) to finish the work = 12 days
Time taken by ( Tom + John) to finish the work = 20 days
Time taken by ( John + Rock) to finish the work = 15 days
Therefore, ( Rock +
Tom)’s 1 day’s work = 1/12
(Tom + John)’s 1
day’s work = 1/20
(John + Rock)’s 1 day’s work = 1/15
Adding, we get:
2(Rock + Tom + John)’s 1 day’s work = ( 1/12 + 1/20 + 1/15 )
= 12/60 = 1/5
(Rock + Tom + John)’s 1 day’s work = 1/10
(Rock + Tom + John) together do the work in = 10 days.
3 men or 5 women can
do a work in 12 days. How long will 6 men and 5 women take to do it?
a.
6 days
b. 5 days c. 4
days d. 3 days
Answer:
5 women = 3 men
Therefore, 6men + 5 women = 6 men
+ 3 men = 9 men
3 men do the work in 12 days
1 men do the work in (12*3) days
9 men do the work in (12*3)/9 days
= 4 days
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