| A man, a woman or a boy can do a piece of work in 3, 4 and 12 days, respectively. The number of boys that must assist one man and one woman to do the work in one day, is |
A) 6
B) 8
C) 9
D) 5
Correct Answer: D
Solution :
| 1 man's 1 day's work \[=\frac{1}{3}\] |
| 1 woman's 1 day's work \[=\frac{1}{4}\] |
| 1 boy's 1 day's work \[=\frac{1}{12}\] |
| Let x boys must be assist. |
| \[\frac{1}{3}+\frac{1}{4}+\frac{x}{12}=1\] |
| \[\Rightarrow \] \[\frac{x}{12}=1-\frac{7}{12}\] |
| \[\Rightarrow \] \[\frac{x}{12}=\frac{5}{12}\]\[\Rightarrow \]\[x=5\] |
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