Aptitude - Time and Work - Discussion

Discussion Forum : Time and Work - General Questions (Q.No. 1)
1.
A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

1
4

1
10

7
15

8
15

Answer: Option
Explanation:

A's 1 day's work = 1 ;
15

B's 1 day's work = 1 ;
20

(A + B)'s 1 day's work = ( 1 + 1 ) = 7 .
15 20 60

(A + B)'s 4 day's work = ( 7 x 4 ) = 7 .
60 15

Therefore, Remaining work = ( 1 - 7 ) = 8 .
15 15

Discussion:
320 comments Page 1 of 32.

Lakshmanan S said:   3 months ago
How come remaining work 1- 7/15? Please explain me.
(46)

Sahil said:   3 months ago
4( 1/15 + 1/20 ) = work done by both of them together

Work Done + Work left =1 =>because the work is 100% completed

4( 1/15 + 1/20 ) + work left = 1;
work left = 1 - (28/ 60);
Then, work left = 8/15;
(24)

Portia said:   3 months ago
How did 1/15 +1/20 turn into 7/60? Someone, please explain.
(24)

NADIPUDI SIRISHA said:   4 months ago
Thank you for explaining the answer @Giri.
(16)

Durga prasad said:   5 months ago
Lcm of 15 and 30 = 60 units.
A's per day work = 60/15 = 4units.
B's per day work = 60/20 = 3units.
A+B's per day work = 4 + 3 = 7units.
A and B together do the work in 4 days.
= 4 * 7 = 28units.
Remaining work = 32/60 = 8/15.
(116)

Giri said:   5 months ago
Just take LCM on 15 and 20 of 60.
Total work 60.

Capacity A 4 and capacity B 3 total 7.
They both worked together for 4 days and completed work 28.
Remaining work 32/60,
So, the Answer 8/15.
(39)

Mish said:   6 months ago
@All.

Why (A+B)'s 4 days of work is calculated?
Why it's not 3,5,6,7 or any other day?
What is the logic behind it?
(9)

Zak said:   7 months ago
How come 7/60? Please explain.
(26)

Dinesh kumar said:   8 months ago
A = 1/15
B = 1/20
(A+B) = 1/15+1/20 = 7/15
The remaining work = 1-7/15 = 8/15.
(25)

Jeevanantham M said:   10 months ago
@Ayansh.

For this;

(A+B) 's work rate = 1/15 + 1/20 = (4/60 + 3/60) = 7/60.
(19)


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