Use Repeated Addition with 3s

Students compute the total of an array with rows of 3 by adding 3 repeatedly (e.g., 3 + 3 + 3 for 3 rows of 3).

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Grade 2 · Rectangular Arrays and Repeated Addition · question 1 of 3

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12 rungs. A star at the top.

Ines spots 2 picnic blankets in the park, with 3 ants on each blanket. How many ants does she see?

How it is taught

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Repeated addition of 3s means adding 3 again and again.

Each group has 3.

Read it: Skip-count the equal groups

3 trays sit in a row, 3 apples on each. You could count every apple from 1 — or skip-count the trays: 3, 6, 9.

Count the apples on 1 tray: 3.
Skip-count a 3 for each tray: 3, 6, 9.
Name the total from the last skip: 3 + 3 + 3 = 9.

Counting every apple from 1 works, but it is slow, and a skipped apple throws the whole count off.

Each tray holds the same 3 apples, so you only need that 3 again, not a new count.

3, 6, 9 are running totals — the last one is how many apples you have.

When every tray is the same, skip-count the trays, not the apples.

Adding the first 2 trays: 3, 6, and answering 6, forgetting the last tray.

There are 3 trays. Keep skip-counting until the last tray: 3, 6, 9.

5 trays, with 3 apples on each. Add the 3s: how many apples? — 15. 5 trays with 3 apples in each: skip-count the trays — 3, 6, 9, 12, 15.

4 rows of 3 = 3 + 3 + 3 + 3

Let's count the dots in this array. There are four rows, and each row has three dots.

The first row has three dots. So we start with three.

The second row also has three dots. Three plus three is six.

The third row adds three more. Six plus three is nine.

The fourth row adds three more. Nine plus three is twelve.

We can write this as three plus three plus three plus three.

Adding three each time gives us three, six, nine, twelve.

Grade 2 · Counting an array by adding 3s

Four rows of three equals twelve. That's repeated addition with threes!

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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