1. A and B together can complete a task in 7 days. B alone can do it in 20 days. What part of the work was carried out by A?
I. A completed the job alone after A and B worked together for 5 days.
II. Part of the work done by A could have been done by B and C together in 6 days.
A. I alone sufficient while II alone not sufficient to answer
B. II alone sufficient while I alone not sufficient to answer
C. Either I or II alone sufficient to answer
D. Both I and II are not sufficient to answer
Answer: Option: A
Explanation:
B's 1 day's work = = 5 ([latex]\frac{1}{20}[/latex]
(A+ B)'s 1 day's work = [latex]\frac{1}{7}[/latex]
I. (A + B)'s 5 day's work = [latex]\frac{5}{7}[/latex]
Remaining work = 1 - [latex]\frac{5}{7}[/latex] = [latex]\frac{2}{7}[/latex]
[latex]\frac{2}{7}[/latex] work was carried by A.
II. is irrelevant.
2. A and B can do a work in 8 days, B and C can do the same work in 12 days. A, B and C together can finish it in 6 days. A and C together will do it in :
A. 4 days
B. 6 days
C. 8 days
D. 12 days
Answer: Option: D
Explanation:
A + B + C)'s 1 day's work = [latex]\frac{1}{6}[/latex]
(A + B)'s 1 day's work = [latex]\frac{1}{8}[/latex]
(B + C)'s 1 day's work = [latex]\frac{1}{12}[/latex]
(A + C)'s 1 day's work = 2 X [latex]\frac{1}{6}[/latex] - [latex]\frac{1}{8}[/latex] + [latex]\frac{1}{12}[/latex]
= [latex]\frac{1}{3}[/latex] - [latex]\frac{5}{24}[/latex]
= [latex]\frac{3}{24}[/latex]
= [latex]\frac{1}{8}[/latex]
3. A and B together can do a piece of work in 30 days. A having worked for 16 days, B finishes the remaining work alone in 44 days. In how many days shall B finish the whole work alone?
A. 30 days
B. 40 days
C. 60 days
D. 70 days
Answer: Option: C
Explanation:
Let A's 1 day's work = x and B's 1 day's work = y.
Then, x + y = [latex]\frac{1}{30}[/latex] and 16x + 44y = 1.
Solving these two equations, we get x = [latex]\frac{1}{60}[/latex] and y = [latex]\frac{1}{60}[/latex]
B's 1 day's work = [latex]\frac{1}{60}[/latex]
4. A takes twice as much time as B or thrice as much time as C to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in:
A. 4 days
B. 6 days
C. 8 days
D. 12 days
Answer: Option: B
Explanation:
Suppose A, B and C take x, [latex]\frac{X}{2}[/latex] and [latex]\frac{x}{3}[/latex] days respectively to finish the work.
Then, [latex]\frac{1}{x}[/latex] + [latex]\frac{2}{x}[/latex] + [latex]\frac{3}{x}[/latex] = [latex]\frac{1}{2}[/latex]
[latex]\frac{6}{x}[/latex] = [latex]\frac{1}{2}[/latex]
x = 12
5. A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. The whole work was completed in :
A. 8 days
B. 10 days
C. 12 days
D. 15 days
Answer: Option: A
Explanation:
(A + B)'s 1 day's work = [latex]\frac{1}{15}[/latex] + [latex]\frac{1}{10}[/latex] = [latex]\frac{1}{6}[/latex]
Work done by A and B in 2 days = [latex]\frac{1}{6}[/latex] x 2 = [latex]\frac{1}{3}[/latex]
Remaining work = 1 - [latex]\frac{1}{3}[/latex] = [latex]\frac{2}{3}[/latex]
Now, [latex]\frac{1}{15}[/latex] work is done by A in 1 day
[latex]\frac{2}{3}[/latex] work will be done by a in 15 x [latex]\frac{2}{3}[/latex] = 10 days.
Hence, the total time taken = (10 + 2) = 12 days