Video: Understanding Place Value When Comparing Numbers

Is 5 + 2 + 1 <, = or > 521?

02:13

Video Transcript

Is five plus two plus one less than, equal to, or greater than 521?

If we look at the two expressions that we’re comparing in this question, we can see why the question is being asked. The first expression is an addition, five plus two plus one. And then, we’re given a number, 521. And if we look at both expressions, we can see something similar about them. They both contain the same digits. We can see a five, a two, and a one. On the right-hand side, our digits make a three-digit number. The five digit is worth five hundreds. The two digit is worth two tens. And the one digit is in the ones place.

Now, if we look at the five, the two, and the one in the first expression, we can see that they’re all worth a number of ones. We’re adding together five ones plus two ones pluse one one. Five plus two plus one equals eight ones altogether. The value of five plus two plus one equals eight. And we can see straightaway that eight is less than 521. Both of our expressions contained the same digits but to give the digits the same value, they needed to be in the same columns. And they’re not.

In the first expression, the five, the two, and the one were all representing a number of ones. But in the second expression, the five represented five hundreds, the two was in the tens place, and only the one was in the ones place. Five plus two plus one makes a total of eight. And eight is less than 521. And so, the correct symbol to use to compare these two expressions is the one that means is less than.

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