Aptitude - Time and Work - Discussion

How did 7/20 come?

How did you get 7/60 please answer in simple method and tell how got 7.

1/15+1/20= 7/60 How ? Please explain me clearly.

@Rashmi, @Satish : 1/15 + 1/20 Now to make the denominator value equal take LCM i.e. ,
= (1*20) / (15*20) + (1*15) / (15*20) Now simplify these,
i.e. , multiply the values i.e. ,
= (20/300) + (15/300).
Now, both the denominator are equal, so you can add the numerator values i.e. , = (20+15) /300 = 35/300,
Now simplifying this i.e. , cancelling both numerator and denominator by 5 (a common value which both will get cancel) ,
We get 7/60. Hope this will help you to understand the problem.

@Swetha why mutiply with (A*TOTAL CAPACITY)?

Thank you sundar nice explanation

How come Remaining work 1-7/15 (note:- why come 1 value )

A=1/15;B=1/20
[A+B]=[1/15+1/20] {1/15*20/20=20/300; 1/20*15/15=15/300}
=20+15/15*20 {cross multiplication}
=35/300 {20+15=35;15*20=300}
=7/60

7/60*4=28/60 {4*7=28}
=7/15

@Esha.

It's not 7/20 its 7/60 and that came after addition of
Both work A and B
A+B= 1/15+1/20=20+15/15*20=35/300=7/60.

Plzz solve this A and B can together finish a work in 30 days. They worked at it for 20 days and then B let.

The remaining work was done by A alone in 20 more days. B alone can do the entire work in.

(a) 48 days (b) 50 days (c) 54 days (d) 60 days.