Maths trivia

Here's a brain teaser for the maths genius' amongst us.......or those that think they are!

6,250 litres of rain collected in 24 hours off 200 sqm roof. How many cm of rain is that!

1cm (10mm) of rain on 1 square metre of roof yields 10L water, therefore divide the litres collected by 10, divide the answer to that by 200, equals 3.125cm or 31.25mm.

We've had about the same over the last 24hrs too!

Wow Megan you made that harder than you had to.

6250 divided by 200 (Sqm roof area) = 31.25mm so 3.125cm

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Edited to appease spoook

Aquila, I do not think "Wow Megan you made that harder than you had to." was a fair comment.
The details given gave the reason for the calculation and not just produced the answer. Stikki now knows how to calculate from Megan but only knows the answer from you. (might have helped had you not hit the shift key when displaying the divide slash for it to come out as a question mark [])

Its a divide sign on my phone....... Maybe just not displaying correctly your end

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But was the roof area flat?

Yes, and if not flat, what was the orientation of the roof and which direction was the rain coming from.
There is a huge difference if you have a west facing roof and the rain is coming from the west, but when it comes from the east, that tank will get a lot less water in it than if the rain was coming from the west

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Neither of your questions are really relevant as the captured water is being measured not the rainfall.

If you know how much rainfall you got I can calculate how much you actually managed to collect.

Megan;461636 wrote: 1cm (10mm) of rain on 1 square metre of roof yields 10L water, therefore divide the litres collected by 10, divide the answer to that by 200, equals 3.125cm or 31.25mm.

We've had about the same over the last 24hrs too!

Haven't checked our gauge but we did get quite a bit judging by the lakes we now have!

Aquila;461683 wrote: Bit of a desperate housewife thing going on here now?

Neither of your questions are really relevant as the captured water is being measured not the rainfall.

If you know how much rainfall you got I can calculate how much you actually managed to collect.

And those questions matter not a jot, because even a rain gauge placed in a good pozi will have more rain hitting one side, than the other, but the measurement is still relevant. Also, 200Msq is still 200Msq whether is it flat or pitched.

You can be assured of the accuracy of 6250L as the tank is 1/4 full now and it was empty. Since it is a 25,000L tank, 25000/4=6250

I like Megan's answer the best, as by showing how she worked it out, shows logical sequence, and knowledge. Just the sort of thing that math's challenges in schools look for. We have an inter school mathex coming up sometime this year.

You're aware the tank is full at the start of the dome, not full to overflowing?

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Aquila;461692 wrote: You're aware the tank is full at the start of the dome, not full to overflowing?

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Yes.

Actually stikki, it does matter what the pitch of your roof is and the direction of the rain but this wont affect the rain gauge at all, if its level is above the surroundings - thats how rain gauges work they can measure wherever the weather comes from.
When we get easterly rain, my water tank on my west sloping roof collects next to no water so orientation and pitch will make a huge difference to what is collected

Stikkibeek;461691 wrote: Also, 200Msq is still 200Msq whether is it flat or pitched.

BUt is the actual roof 200 sq/m or is the house 200 sq/m?
A 200 sq/m house with a 45degree roof plus over hangs will measure alot more than 200 sq/m[]

skyline_glenn;461708 wrote: BUt is the actual roof 200 sq/m or is the house 200 sq/m?
A 200 sq/m house with a 45degree roof plus over hangs will measure alot more than 200 sq/m[]

I see what you write, but would you say to your maths teacher; to the question what is 12x4?
"Sir is the actual figure 12, or does it overhang due to a variation and therefore make 14?" I didn't give you any extranious information, with the exception of 24 hours, which while making the problem to solve more interesting, is unimportant in the equation.