Add a Two-Digit Number and a Multiple of Ten

Students will add a two-digit number and a multiple of 10 within 100 using place value understanding. Students learn that adding multiples of ten only changes the tens digit, not the ones digit.

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Grade 1 · Comparing and Computing with Two-Digit Numbers · question 1 of 3

0 of 12

12 rungs. A star at the top.

8 + 40 =

How it is taught

0:00 of 3:04

Adding tens changes the tens digit.

The ones digit stays the same.

Read it: Add or take away tens: jump 10 at a time

36 + 50: 50 is 5 tens. Jump 10, 5 times from 36: 46, 56, 66, 76, 86. To take 50 away, jump back: 86 − 50 = 36.

Say how many tens: 50 is 5 tens.
Jump 10 that many times: forward to add, back to take away.
Say where you land: 36 + 50 = 86, and 86 − 50 = 36.

Each jump of 10 changes the tens digit by 1.

The ones digit does not change, because no ones are added or taken: it stays 6.

So adding or taking away tens is counting by tens from the start.

Count by tens from the start, forward or back. The ones stay the same.

Adding 5 to the ones: 36 + 50 = 41.

50 is 5 tens, not 5 ones. Jump 10, 5 times: 86.

Start at 53 and jump 10, 3 times. Where do you land? — 83. 63, 73, 83. So 53 + 30 = 83.

23 + 40

You have twenty-three stickers. Your friend gives you forty more. How many do you have now?

Let's stack them up. Twenty-three plus forty.

First, look at the ones place. We have three ones, and forty has zero ones.

Three plus zero is three. The ones digit doesn't change!

Now the tens place. Twenty-three has two tens, and forty has four tens.

Two tens plus four tens is six tens. Write six.

Grade 1 · Adding tens keeps the ones the same

See? Adding a multiple of ten only changes the tens digit.

Twenty-three plus forty is sixty-three. You have sixty-three stickers!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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