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aniked [119]
3 years ago
15

One pump can fill a reservoir in 60 hours. Another pump can fill the same reservoir in 80 hours. a third can empty the reservoir

in 90 hours. If all three pumps are operating at the same time, how long will it take to fill the reservoir?
Mathematics
2 answers:
steposvetlana [31]3 years ago
7 0

one pump, let's call it A, fills the reservoir by 1/60 every hour. Now, B fills it by 1/80 every hour. C empties it by 1/90 every hour. All three are on, so now we combine them into one function: t(1/60 + 1/80 - 1/90) = 1, where t = the time it takes to fill it, and 1 is just our "reservoir finally filled" marker.

isolate t onto one side and we see t = 720/13 exactly, or approximately 55.38 hours. let me know if this is the wrong answer but I'm pretty sure it is correct!

11111nata11111 [884]3 years ago
4 0

Answer:

1/time needed = 1/time of 1st pump + 1/time of 2nd pump - 1/time of 3rd pump

1/t = 1/t1 + 1/t2 - 1/t3

1/t = 1/60 + 1/80 - 1/90

1/t = 12/720 + 9/720 - 8/720

1/t = 13/720

t = 720/13 hours = 55.38 hours = 55 hours 23 minutes

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Answer:

Susan has 8 numbers belonging to just one list.

Step-by-step explanation:

Susan's 3 lists have 10 numbers each = 10 x 3 =  30 numbers

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Then, there are 5 numbers on 2 lists only = 5 x 2 = 10 numbers

The numbers on just one list = 18 - 10 = 8 numbers

Or

                                    List 1     List 2    List 3   Total

Numbers on each list    10           10         10      30

Numbers on 3 lists        -4           -4         -4        12

Numbers on 2 lists        -5           -5        -0        10

Numbers on 1 list only    1             1          6         8

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