Question Video: Finding the Tens Digit of the Result of Adding Three-Digit Numbers to Two-Digit Numbers Mathematics

If I add together 436 and 60, what will the tens digit of the sum be?


Video Transcript

If I add together 436 and 60, what will the tens digit of the sum be?

This is an interesting question because it starts off by looking like we need to add together 436 and 60. But as we read the rest of the question, we can see that we’re not being asked for the sum of these two numbers. We’re being asked what the tens digit in the sum is going to be. And you might think to yourself, “Well, I’m gonna have to work out the answer and then just look at what the tens digit is.” But there’s a quicker way to solve the problem, and it involves us understanding what it means to add a multiple of 10 to a three-digit number. So, let’s have a go at solving this problem the quick way.

And it’s not that difficult; it just involves us understanding the place value of the numbers that we’re adding. So, if we think about the number we’re starting with, 436 contains four 100s, three 10s, and six ones. And the number that we’re adding to this contains six 10s and zero ones and, of course, zero 100s as well. Now, the really important bit about what we’ve just said is this digit here. The number that we’re adding on to 436 contains six 10s. It doesn’t contain any hundreds, doesn’t contain ones, just six 10s because six tens equals 60.

Now, as we’ve said already, our starting number 436 has got three 10s. So if we already have three 10s and we’re adding on six 10s, what will the tens digit of the sum be? Well, we know that three plus six equals nine. So, three 10s plus six 10s is going to make nine 10s. Our answer is going to have the digit nine in the tens place. So, although we don’t have to, let’s just write down what the sum would be. It’s still going to have four 100s, and it’s still going to have six ones. Those digits aren’t going to change. But the three tens that we started with are now going to become nine 10s. 436 plus 60 equals 496.

We’ve used our knowledge of place value here to work out what the tens digit is going to be. If we add 60 to a number that has three 10s — in this question, it was the number 436, but, you know, it could have been any number at all — we found that the answer will contain nine 10s. So, the tens digit of the sum of these two numbers is nine.

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