Video: Multiplying Integers Involving Masses

Mason bought 10 apples from a grocery store. If the average mass of 1 apple is 122 grams, approximate the total mass of Mason’s apples.

02:52

Video Transcript

Mason bought 10 apples from a grocery store. If the average mass of one apple is 122 grams, approximate the total mass of Mason’s apples.

Let’s start by underlining the important information. And we’ll sketch a bar model to help us understand how to find the answer. So the first thing we’re told is that Mason bought 10 apples. So here are Mason’s 10 apples. Now, apples come in all sorts of shapes and sizes. But we’re told that the average mass of one apple is 122 grams. So we can fill in the bar model to show this. And our question asked us to approximate the total mass of Mason’s apples.

Why does the question ask us to approximate the answer? Why doesn’t it ask us to calculate or to find the exact amount? As we have said already every apple is different. And so we’re using an average mass. And so if Mason took 10 apples all slightly different and put them on a set of weighing scales, we’re being asked to find the approximate mass not the exact amount. So how do we find out 10 lots of 122 grams?

One way to find the answer will be to add 122 10 times. But this will take a while. And of course, we know if we add the same number lots of times, we can multiply instead. And so we can find our answer by multiplying 122 by 10. How do we multiply numbers by 10? Well, when any number is multiplied by 10, the digits in that number shift one place to the left. This is because each digit is now worth 10 times as much as it was before.

So instead of the digit one representing 100, it’s now worth 10 times as much. So it’s now worth 1000. And instead of the two in the tens column being worth tens, it’s now worth 10 times as much, hundreds. So that digit shifts one place too. And the two ones are now worth two tens. We write a zero in the ones column as a placeholder to show that everything is shifted along one column. And so by multiplying 122 by 10, we found the answer. So if the average mass of one apple is 122 grams and Mason has bought 10 of them, the approximate total mass is 1220 grams.

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