Video: Estimating the Suitable Quantity Required to Perform a Certain Action

Leo showers for 10 minutes. Has he used about 80 cups or 150 gallons of water?

03:33

Video Transcript

Leo showers for 10 minutes. Has he used about 80 cups or 150 gallons of water?

This question is getting us to estimate capacity. The amount of water that Leo uses if he showers for 10 minutes. We’re given two choices, and they’re both different units of measurement. One is 80 cups and the other one 150 gallons. Which is more likely to be the amount of water that Leo uses when he showers? You may think this looks like it could be an easy question. After all, there are only two choices. It’s either one or the other. It is actually quite a tricky question to answer for three reasons.

The first reason is the units of measurement that I mentioned. We don’t use gallons that often in everyday life, so they’re quite hard to visualize. And even though we do use cups, to imagine what 80 cups is like is fairly tricky.

The second and third reasons why this is a tricky question is to deal with the fact that Leo’s having a shower. If we think about how a shower works compared with a bath, the water comes out as spray. It doesn’t come out all in one go. And so, it’s much harder to work out what 80 cups or 150 gallons might look like if it’s coming out of a showerhead as spray.

And, the third reason why this is tricky is if you think about a bath, when you fill a bath with water, you can see what all that water looks like, all the water that you’ve used. It sits in the bath until you’re finished. But, with a shower, it doesn’t collect anywhere. It flows down the plug hole. And so, this is another reason why this is quite tricky to visualize.

So to estimate our answer, we’re gonna have to use some facts we already know to help us. Something we can visualize easily is what one pint looks like. Here’s one pint of milk. And this picture represents one gallon. You may have seen big water containers that contain one gallon. Now, one gallon is the same as eight pints. This can help us visualize quite how much liquid there is in one gallon. Now, imagine 150 of these large water containers. Is this the amount of water that Leo has used as he showers? Or is it more likely that he’s used 80 cup fulls?

Remember that the water doesn’t come out all in one go. It comes out as a spray, doesn’t it? We can see here that 150 gallons is a lot of water. The best estimate for the amount of water that Leo uses, if he showers for 10 minutes, is 80 cups. Here is an interesting fact that you could’ve used if you’d have known it. You may already know that having a shower uses less water than a bath. But, maybe you didn’t know that a bath contains about 30 to 40 gallons of water. So, 150 gallons of water would be five bath fulls. Leo would need to be in the shower for a lot longer than 10 minutes to use five bath fulls of water. The correct answer and the best estimate is 80 cups.

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