A and B together can do a piece of work in 15 days, while B alone can finish it 20 days. In how
many days can A alone finish the work ? (Page 3/5)
Example 5: A and B can do a piece of work in 15 days and 20 days respectively. Find:
(i) The work done by A in 3 days .
(ii) The work left after A has worked for 3 days.
(iii) The number of days that B will take to complete the remaining work.
Answers
Step-by-step explanation:
let’s say entire work is done means he/she has done 100% of the work.
Reasonably, according to the statement,A alone can complete only 5% of the work per day. (100/20=5)
A +B worked for 15 days→ A completed 15*5=75% of the work . Thus , rest 25% work has been completed by B in 15 days.
B has done 25% of the work in 15 days. Thus, he would take 60 days to complete the whole work. (15 *4=60)
Second way:
If you are really good at maths: It is a simple equation.First consider 1 day of work.
A→1/20
B→ Don’t know
A+B=1/15.
Thus, 1/20+1/B=1/15. If you solve this B would get 60. ( you need to be very strong in maths by watching the equation to find out 60 for B).
So in one day B would complete 1/60th work . To complete entire work he would take 60 days.