If 15 oxen or 20 cows can eat the grass of a field in 80 days,then in how many…
2024
If 15 oxen or 20 cows can eat the grass of a field in 80 days,then in how many days will 6 oxen and 2 cows eat the same grass?
- A.
300
- B.
104
- C.
160
- D.
120
Attempted by 41 students.
Show answer & explanation
Correct answer: C
Key idea: compute each animal's daily grazing rate and add them.
One ox's rate = 1/(15 × 80) = 1/1200 of the field per day.
One cow's rate = 1/(20 × 80) = 1/1600 of the field per day.
Combined rate of 6 oxen and 2 cows = 6 × (1/1200) + 2 × (1/1600) = 1/200 + 1/800.
Simplify: 1/200 + 1/800 = 4/800 + 1/800 = 5/800 = 1/160 of the field per day.
Therefore the time required = reciprocal of rate = 160 days.
Answer: 160 days.