If Jenna can build a tractor in 9 hours, Thomas can build a tractor in 7 hours, Rachel can build a tractor in 5/2 hours, and Paul can build a tractor in 2 hours, how long will it take them to build 15 tractors if all four start building tractors at midnight, Rachel leaves after 3 hours (3 am), Jenna leaves after 6 hours (6 am), and Rachel returns after 9 hours (9 am)

Question

Mathematics

Dominique Wang

20 April, 23:26

If Jenna can build a tractor in 9 hours, Thomas can build a tractor in 7 hours, Rachel can build a tractor in 5/2 hours, and Paul can build a tractor in 2 hours, how long will it take them to build 15 tractors if all four start building tractors at midnight, Rachel leaves after 3 hours (3 am), Jenna leaves after 6 hours (6 am), and Rachel returns after 9 hours (9 am)

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Answers (1)

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Mariana Marshall · Answer 1

Around 16 hours

(16 hours, 2.74 minutes)

Step-by-step explanation:

In 3 hours,

Rachel has managed: 3 : 5/2 = 6/5

In 6 hours,

Jenna has managed: 6 : 9 = ⅔

Till 9 am,

Thomas and Paul have been woking and maneged:

(9 : 7) : (9 : 2) = 81/14

Total works done in first 9 hours:

6/5 + 2/3 + 81/14 = 1607/210

Remaining work:

15 - 1607/210

= 1543/210

Rachel, Paul and Thomas complete this remaining job together in next 't' hours

(t/2.5) + (t/2) + (t/7) = 1543/210

73t/70 = 1543/210

t = 7.0456621 hours

Or 7 hours 2.74 mins

Overall, it will take them around 9+7 = 16 hours to complete the task

They'll be done at 1600

Which is 4 pm