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:
100 comments Page 3 of 10.
Xyx said:
9 years ago
How it will 7/12-1/2=1/12?
(1)
Kavit vaishnav said:
1 year ago
A takes 4 hours, 1 hour work = 25%.
For A+C = 2 hours =100% work.
A's part = 50%(for 2 hours),
Remaining part done by C 50% in time 2 hours. So C also does 25% in 1 hour.
Now B+C = 3 Hours = 100% work.
C's part = 3*25% = 75% in 3 hours.
B's part = remaining work = 25% in 3 hours.
So, B' s efficiency = 100% in 12 hours.
For A+C = 2 hours =100% work.
A's part = 50%(for 2 hours),
Remaining part done by C 50% in time 2 hours. So C also does 25% in 1 hour.
Now B+C = 3 Hours = 100% work.
C's part = 3*25% = 75% in 3 hours.
B's part = remaining work = 25% in 3 hours.
So, B' s efficiency = 100% in 12 hours.
(1)
Gayathri said:
3 months ago
A = 1/4
B + C = 1/3 ----> eq(1)
A + C = 1/2 ----> eq(2)
Sub eq(1)-eq(2).
B + C - A - C = 1/3 - 1/2,
B - A = -1/6,
B = -1/6 + 1/4( where A=1/4).
B = 1/12.
Hence B alone takes 12 hours.
B + C = 1/3 ----> eq(1)
A + C = 1/2 ----> eq(2)
Sub eq(1)-eq(2).
B + C - A - C = 1/3 - 1/2,
B - A = -1/6,
B = -1/6 + 1/4( where A=1/4).
B = 1/12.
Hence B alone takes 12 hours.
(1)
A K BURNWAL said:
3 months ago
A- 4 hours, a's 1 hour = 1/4.
B + C- 3 hours, B + C's 1 hour = 1/3,
A + C- 2 hours, A + C'1 hour = 1/2,
C's 1 hour = 1/2 - 1/4 = 1/4.
B = 1/3 - 1/4 = 1/12.
So, B takes 12 hours to complete work.
B + C- 3 hours, B + C's 1 hour = 1/3,
A + C- 2 hours, A + C'1 hour = 1/2,
C's 1 hour = 1/2 - 1/4 = 1/4.
B = 1/3 - 1/4 = 1/12.
So, B takes 12 hours to complete work.
(1)
Ashim said:
1 decade ago
4A = 3 (B + C) = 2 (A + C).
4A = 2A + 2C, A = C.
3B + 3C = 2A + 2C.
3B = C.
Or 3B = A.
If A takes 4 hours to complete the work than B takes 12 hours.
4A = 2A + 2C, A = C.
3B + 3C = 2A + 2C.
3B = C.
Or 3B = A.
If A takes 4 hours to complete the work than B takes 12 hours.
Prajwal said:
1 decade ago
A = 1/4.
B + C= 1/3.
A + C= 1/2.
B = ?
C = 1/2 - A.
C = 1/2 - 1/4 = 1/4.
B = 1/3 - C.
B = 1/3 - 1/4.
B = 1/12.
B takes 12 hrs.
B + C= 1/3.
A + C= 1/2.
B = ?
C = 1/2 - A.
C = 1/2 - 1/4 = 1/4.
B = 1/3 - C.
B = 1/3 - 1/4.
B = 1/12.
B takes 12 hrs.
Anil said:
1 decade ago
By solving this three equation, we will get the answer.
1/A = 1/4.
1/B + 1/C = 1/3.
1/A + 1/C = 1/2.
1/A = 1/4.
1/B + 1/C = 1/3.
1/A + 1/C = 1/2.
Anjum said:
1 decade ago
Thank you everyone for the clear explanation.
Chiru said:
1 decade ago
Thank you everyone for the clear explanation.
Reshma said:
1 decade ago
A = 1/4.
B + C = 1/3.
A + C = 1/2.
Subtract the above 2 equations we get,
B - A = 1/3 - 1/2,
B - A = -1/6,
B = -1/6 + 1/4,
B = 1/12,
So, B takes 12 hours to complete the work.
B + C = 1/3.
A + C = 1/2.
Subtract the above 2 equations we get,
B - A = 1/3 - 1/2,
B - A = -1/6,
B = -1/6 + 1/4,
B = 1/12,
So, B takes 12 hours to complete the work.
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