Discussion
A man can plough a field alone in 20 days. His wife can plough it in 25 days. When they plough the field with their son they can plough it in 5 days. How many days would the son take if he were to plough the field alone?
Answer: B
The son alone would take \(9\frac{1}{11}\) days.
Work out how much of the field each person ploughs in one day and subtract the parents' share from the family's total.
\[ \begin{aligned} \text{son} &= \frac{1}{5} - \frac{1}{20} - \frac{1}{25} \\ &= \frac{20 - 5 - 4}{100} \\ &= \frac{11}{100} \end{aligned} \]
So the son ploughs \(\frac{11}{100}\) of the field a day and needs \(\frac{100}{11} = 9\frac{1}{11}\) days.
Check that the three together finish in 5 days:
\[ \begin{aligned} \frac{1}{20} + \frac{1}{25} + \frac{11}{100} &= \frac{5 + 4 + 11}{100} \\ &= \frac{20}{100} = \frac{1}{5} \end{aligned} \]
The other options differ only in the whole number, so the subtraction alone decides them.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development