You have an irrigation pond with a constant flow of water into it. You are pumping water out to some "Big Gun" sprinklers. There is already some water in the pond.
If you turn 10 Sprinklers on… your pond will be "dry" (the pump will lose it's prime and shut down) in 2.5 hours.
If you turn 7 Sprinklers on… your pond will be "dry" in 6 hours and 15 minutes.
How long will 6 sprinklers run?
How many sprinklers can you run to equalize with the incoming water (the pond won't get any fuller nor will it go dry)?
quick look at it.
i think 4 sprinklers equals the inflow. (haven't worked it out because can't remember how to solve simultaneous equations)
and 6 sprinklers will be dry in 7 hrs 30 minutes.
didn't really work anything out tomk especially not what the inflow is and what each sprinklers output was, (need to do some googling when i have time to learn how to work with multiple equations again) so just had a quick look and saw the difference between 10 and 7 sprinklers was 225 minutes divided that by 3 which works out to 75 minutes longer for every sprinkler removed. so 6 sprinklers should be 7hrs and 30 minutes if my thinking was correct, can't remember why i thought 4 sprinklers for other answer, my instant thought was five but then i edited it and changed it to four for some reason .
so not surprised if the inflow = sprinklers was wrong but am a bit if the the 7 hrs and 30 minutes answer was wrong.
not to worry tho it's just a first answer to get things rolling.
i'll spend a bit more time later in the week(unless it gets answered first, fingers crossed ) looking at my logic and trying to figure out if i'm correct when i think
outflow/10=pond+(150x inflow)
and
outflow/7=pond+(375x inflow)
and
outflow/12 = pond+(0x inflow)
and then with googles help learn how to work out simultaneous equations again to find the constants for outflow, pond and inflow.
what no-one has answered this yet..
ok will try and find my thinking cap and see if i can come up with the answer in the next few hrs.
a sprinkler must output less than the inflow otherwise the number of sprinklers needed to equal inflow would be less than 1 which is impossible, so after x sprinklers are working to equal the inflow the rest are just emptying the pond and where my logic for the 7hrs 30minutes answer was wrong.
mmmm think my brains working today, so might have a chance of actually finding the answers.
think i got it.
5 pumps = flow
10-5=5 pumps empty pond 2 1/2 x faster than 7-5=2 pumps. 5/2
2 1/2 x150 minutes is 375 minutes.
so 10-5=5 pumps empty the pond 5 x faster than 6-5=1 pump. 5/1
5 x 150 minutes is 750 minutes or 12.5 hrs.
12.5 hrs
5 pumps
) looking at my logic and trying to figure out if i'm correct when i think
outflow/10=pond+(150x inflow)
and
outflow/7=pond+(375x inflow)
and
outflow/12 = pond+(0x inflow)
and then with googles help learn how to work out simultaneous equations again to find the constants for outflow, pond and inflow.
ok will try and find my thinking cap and see if i can come up with the answer in the next few hrs.
a sprinkler must output less than the inflow otherwise the number of sprinklers needed to equal inflow would be less than 1 which is impossible, so after x sprinklers are working to equal the inflow the rest are just emptying the pond and where my logic for the 7hrs 30minutes answer was wrong.
mmmm think my brains working today, so might have a chance of actually finding the answers. 
was one of those that looked hard but was quite easy once i found my thinking cap. 
