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Mentally Add 10 to a Number from 100 to 900

Students mentally add 10 to a three-digit number by increasing the tens digit by one while keeping hundreds and ones unchanged (e.g., 10 more than 347 is 357).

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Mentally Add 10 to a Number from 100 to 900

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

0 of 12

12 rungs. A star at the top.

54 + 10 = .

How it is taught

0:00 of 3:07

Ten more changes the tens place.

Ones stay the same unless tens fill up.

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.

  1. Find where you start on the line.
  2. Hop 10 or 100 at a time: forward to add, back to take away.
  3. 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.

243 + 10 = ___ — 253. 1 jump of 10 from 243 lands on 253 — 1 mark along, not 10 little steps.

347 + 10

You have 347 stickers. A friend gives you 10 more. How many do you have now? Let's solve it in our heads!

Here's our number: three hundred forty-seven. It has three hundreds, four tens, and seven ones.

When we add ten, only ONE place changes — the tens place. Right now it's four.

Adding ten just means one more ten. Four tens plus one ten makes five tens.

10 more than 347 = ?347 stickers + 10 more...let's do it in our heads!hundredstensones347+ 1 ten54 → 5same ✓same ✓347 + 10 = 357ANSWER357stickers
Grade 2 · Adding 10 only bumps the tens digit by one

So the tens digit changes from four to five.

The hundreds digit doesn't change — still three.

And the ones digit doesn't change either — still seven.

Three hundred forty-seven plus ten is three hundred fifty-seven. Easy mental math!

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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