# Lesson Video: Adding Tens on a Number Line Mathematics • 1st Grade

In this video, we will learn how to add multiples of ten to a two-digit number using a number line with numbers up to 100.

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### Video Transcript

Adding 10s on a Number Line

In this video, we will learn how to add multiples of 10 to a two-digit number using a number line with numbers up to 100.

A multiple of 10 is a number we can divide by 10 without any remaining. We know that there is one 10 in the number 10. There are two 10s in 20, three 10s in 30, and four 10s in 40. All of these numbers are multiples of 10. 10, 20, 30, 40, 50, 60, 70, 80, and 90. 10, 20, 30, 40, 50, 60, 70, 80, 90, these all are multiples of 10.

In this video, we’re learning how to add multiples of 10 to two-digit numbers. Two-digit numbers have two digits, a tens digit and a ones digit. The tens digit in the number 33 is a three. The three digit is worth three 10s, and we know that three 10s are worth 30. And the ones digit in the number 33 is worth three ones. If we were to add 50 to the number 33, we’d be adding five more 10s and no ones.

How can we use a number line to help us add five 10s? We could skip count in 10s. We need to count forward on the number line five 10s starting from the number 33. If we add another 10 to 33, we’ll have four 10s. We’ve added one 10 to the number 33. We have to add five altogether. One, two, three 10s, four 10s, five 10s. 33 plus 50 is 83. Watch what happens to the tens digit if we start at 33 and skip count forward 50. 10, 20, 30, 40, 50. Did you notice what happened to the ones digit each time we added 10? They stayed the same. We’re just adding 10s. When we add a multiple of 10 to a two-digit number, the tens digit increases and the ones digit stays the same.

We’re going to try some practice questions now where we can add multiples of 10 to two-digit numbers using a number line.

Find 10 more than 62. Use the number line to help you.

In this question, we have to add 10 to the number 62. We’re given a number line to help. And the number 62 is marked. 62 is a two-digit number. It has six 10s and two ones. We can see from the number line that the number 62 is two more than 60. If we have to find 10 more than 62, we just need to add one 10. So instead of having six 10s, our number will have seven 10s. We can see from the number line if we add 10 to 62, we get 72. 62 is two more than 60, and 72 is two more than 70. The number 62 has two ones, and the number 72 has two ones. The ones digit didn’t change. When we counted forward 10, the tens digit increased by one. 10 more than 62 is 72.

Use the number line to calculate 90 plus 10.

In this question, we have to calculate 90 plus 10. And we’re told to use the number line to help. Here’s the number 90 on the number line. And the numbers on the number line increase by 10 each time. 10, 20, 30, 40, 50, 60, 70, 80, 90. So to calculate 90 plus 10, we just need to add one more 10. 10 more than 90 is 100. 90 plus 10 is 100. We used the number line to calculate 90 plus 10.

Use a number line to find 50 more than 22. Hint: Count in 10s.

In this question, we have to use the number line to find 50 more than 22. And we’re told to count in 10s. The number 22 has already been marked on the number line. 22 is a two-digit number. It has two 10s and two ones. We’re adding 50 to the number 22. The number 50 is a multiple of 10. There are five 10s in the number 50 and no ones. 22 has two 10s. And we have to add five more 10s. 10, 20, 30, 40, 50.

Did you notice what happened to the two digits as we counted forward five 10s on the number line? 22, 32, 42, 52, 62, 72. The tens digit increased, but the ones digit stayed the same. We had two 10s, and we counted forward five more 10s. Two plus five is seven, so two 10s plus five 10s is seven 10s. The tens digit increased by five. 50 more than 22 is 72. We started at number 22 on the number line, and we counted forward in 10s. 22 and five more 10s is 72.

What have we learned in this video? We’ve learned that when we add a multiple of 10 to a two-digit number, the tens digit increases and the ones digit doesn’t change.