# Video: AQA GCSE Mathematics Foundation Tier Pack 4 • Paper 2 • Question 15

There are 439 gallons of water in a pond. 1 gallon = 8 pints. 1 pint = 570 millilitres. Use the approximations above to show that the pond contains approximately 2000 litres of water.

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### Video Transcript

There are 439 gallons of water in a pond. One gallon equals eight pints. One pint equals 570 millilitres. Use the approximations above to show that the pond contains approximately 2000 litres of water.

So therefore, the first thing we’re gonna do is use the fact that we know that one gallon is equal to eight pints. And if we have 439 gallons of water, then we want to work out how many pints this is going to be. Well, if we had one gallon and we want 439 gallons, then we’re gonna have to multiply this by 439. So therefore, if we want to work out how many pints this is going to be, we’re gonna multiply eight by 439. So this is gonna give us a total of 3512 pints. And that’s what we get when we multiply eight by 439. Okay, great. So we now know what our gallons are in pints.

So now, what we want to do is convert our 3512 pints into millilitres. And to do that, we’re gonna use the conversion that one pint is equal to 570 millilitres. So therefore, to work this out, what we’re gonna do is multiply each side of the conversion by 3512 because that’s what number of pints are. So when we do that, we’re gonna multiply 570 by 3512. So this is gonna give us that 3512 pints is equal to 2001840 millilitres. So have we finished here? No, because what we want to do is show that the pond contains approximately 2000 litres of water. And we’re currently in millilitres. So now, what we want to do is convert to litres.

Well, now what we’re gonna do is use an exact conversion. And that is that one litre is equal to 1000 millilitres. So therefore, we can say that 2001840 millilitres is gonna be equal to 2001840 divided by 1000 litres. And that’s because, as we said, one litre is 1000 millilitres. So if we want to convert back, we’re gonna divide by 1000. Well, this is gonna give us 2001.84 litres. So we know that 439 gallons of water is equal to 2001.84 litres. But we’re asked to show that it contains approximately 2000 of litres within the pond. Well, 2001.84 litres is approximately 2000 litres.

So therefore, we’ve used the approximations and shown that the pond contains approximately 2000 litres of water.