Two college students have started their own business building computers from kit

Question

Two college students have started their own business building computers from kits. Working alone, one student can build a computer in 12 h. When the second student helps, they can build a computer in 4.8 h. How long would it take the second student, working alone, to build the computer? hr Three machines are filling water bottles. The machines can fill the daily quota of water bottles in 42 h, 48 h, and 56 h, respectively. How long would it take to fill the daily quota of water bottles with all three machines working? hr

Explanation / Answer

7. Let second student working alone take X hours to build the computer.

Then according to the information given in the question, we get:

1/12 + 1/X = 1/4.8

1/X = 1/4.8 - 1/12

1/X = (15 - 6) / 72

1/X = 9/72

1/X = 1/8

X= 8 hours

Therefore, second student working alone to build the computer will take 8 hours.

8. Let time taken by all the three machines working together to fill the daily quota of water bottles be Y hours.

Then according to the information given in the question, we get:

1/Y = 1/42 + 1/48 + 1/56

1/Y = (8 + 7 + 6)/336

1/Y = 21/336

1/Y = 1/16

Y = 16 hours.

Therefore, time taken by all the three machines working together to fill the daily quota of water bottles will be 16 hours.

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