Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 7)
7.
A can do a piece of work in 4 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?
Answer: Option
Explanation:
| A's 1 hour's work = | 1 | ; |
| 4 |
| (B + C)'s 1 hour's work = | 1 | ; |
| 3 |
| (A + C)'s 1 hour's work = | 1 | . |
| 2 |
| (A + B + C)'s 1 hour's work = |  |
1 | + | 1 |  |
= | 7 | . |
| 4 | 3 | 12 |
| B's 1 hour's work = | |
7 | - | 1 | |
= | 1 | . |
| 12 | 2 | 12 |
B alone will take 12 hours to do the work.
Discussion:
96 comments Page 2 of 10.
Asha said:
1 decade ago
There is one more method for this question, a shortcut formula. A theorem says 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 the work in xy/y-x days.
Therefore for AC pair C's work hrs = 4*2/4-2= 4 hrs
now for BC pair B's work hrs = 4*3/4-3 = 12 hrs :)
Therefore for AC pair C's work hrs = 4*2/4-2= 4 hrs
now for BC pair B's work hrs = 4*3/4-3 = 12 hrs :)
Ankur said:
1 decade ago
B+C=1/3
A+C=1/2
A+C-(B+C)=1/2-1/3
A-B=1/6
B=A-1/6
B=1/4-1/6
B=1/12
ie 12 is the ans
A+C=1/2
A+C-(B+C)=1/2-1/3
A-B=1/6
B=A-1/6
B=1/4-1/6
B=1/12
ie 12 is the ans
Arjun said:
1 decade ago
Total =4
b&c =3...1
a&c= 2...2
we have to find c so 1 c is 3 therefore 3*4=12
Hey guys let me know if i am correct.
b&c =3...1
a&c= 2...2
we have to find c so 1 c is 3 therefore 3*4=12
Hey guys let me know if i am correct.
Avinash said:
1 decade ago
A's 1day wrk------>1/4
B+C's 1day wrk---->1/3
A+C's 1day wrk---->1/2
(A+C)-A=1/2-1/4=1/2 ie.. c=1/4
so B+1/4=1/3--->b=1/12
B+C's 1day wrk---->1/3
A+C's 1day wrk---->1/2
(A+C)-A=1/2-1/4=1/2 ie.. c=1/4
so B+1/4=1/3--->b=1/12
Rajin said:
1 decade ago
A = 1/4
B+C = 1/3
A+C = 1/2
A+B+C = 1/4+ 1/3 = 7/12
TO FIND B'W WORK
A+B+C - (A+C) = 7/12 - 1/2 = 1/12
B+C = 1/3
A+C = 1/2
A+B+C = 1/4+ 1/3 = 7/12
TO FIND B'W WORK
A+B+C - (A+C) = 7/12 - 1/2 = 1/12
Shro said:
1 decade ago
Thanku hindu:).
Aditya said:
1 decade ago
The above methods are enough to solve this problem...but when i got this question i thought to convert all hours into days...although its a very time consuming...but i got the answer...i am just a beginner...so satisfied with it
1 day=24 hours
1/24 day=1 hour
i/6 day=4 hour....i hope you got my point...but its time consuming so don't use this method...i shared it because...i want to tell you ...what strikes on my mind.
1 day=24 hours
1/24 day=1 hour
i/6 day=4 hour....i hope you got my point...but its time consuming so don't use this method...i shared it because...i want to tell you ...what strikes on my mind.
Arun said:
1 decade ago
Just simply i know that A's is 1/4
B+C is 1/3
So do it
1/3 - 1/4
And u get 1/12
B's work 12 hour
B+C is 1/3
So do it
1/3 - 1/4
And u get 1/12
B's work 12 hour
Kumar said:
1 decade ago
A =1/4 (A's ONE HOUR WORK)
B+C =1/3 (B+C's ONE HOUR WORK)
A+C =1/2 (A+C's ONE HOUR WORK)
C =1/2-A
B+1/2-1/4=1/3 (submitting c value in b+c=1/3 for value of b)
B=1/3-1/2+1/4
B=1/12
B+C =1/3 (B+C's ONE HOUR WORK)
A+C =1/2 (A+C's ONE HOUR WORK)
C =1/2-A
B+1/2-1/4=1/3 (submitting c value in b+c=1/3 for value of b)
B=1/3-1/2+1/4
B=1/12
Sireesha said:
1 decade ago
[(b+c)=1/3]-[(a+c)=1/2]
=> b=1/12
=>b's time= 12hrs
=> b=1/12
=>b's time= 12hrs
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