Mentally Subtract 10 from a Number from 100 to 900

Students mentally subtract 10 from a three-digit number by decreasing the tens digit by one while keeping hundreds and ones unchanged (e.g., 10 less than 347 is 337).

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Grade 2 · Mental Math: Adding and Subtracting 10 and 100 · question 1 of 3

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12 rungs. A star at the top.

230 − 10 =

How it is taught

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Ten less lowers the tens digit.

Ones stay the same unless you regroup.

Read it: Hop by ten or a hundred

You are on 30 on the number line. 3 hops of ten forward land on 60. A hop of a hundred works the same way: it lands on the next hundred.

Find where you start on the line.
Hop 10 or 100 at a time: forward to add, back to take away.
Count the hops: 30 + 30 = 60.

Counting 31, 32, 33 all the way to 60 works, but it is slow and easy to lose track.

Each hop lands on the next tens or hundreds tick, so you skip the numbers in between.

You already know 30 plus 10 is 40, so a hop replaces counting 31 through 39.

To add or take away tens or hundreds, hop 10 or 100 at a time along the line.

Making three hops but landing on 50, because you counted 30 as a hop.

30 is where you start. The first hop lands on 40, then 50, then 60.

223 − 10 = ___ — 213. 1 jump back of 10 from 223 lands on 213 — 1 mark along, not 10 little steps.

10 less than 347

What is ten less than three hundred forty-seven? Let's figure it out in our heads — no counting needed.

Here is three hundred forty-seven. It has three hundreds, four tens, and seven ones.

When we subtract ten, only one digit changes — the tens digit.

We have four tens. One less than four is three.

So the four becomes a three.

Grade 2 · Subtracting 10 mentally

The hundreds digit doesn't change — still three.

The ones digit doesn't change either — still seven.

Ten less than three hundred forty-seven is three hundred thirty-seven!

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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