Use Repeated Addition to Find the Total in an Array

Students will use repeated addition to find the total number of objects in a rectangular array with up to 5 rows and 5 columns. They will write an addition equation that represents the equal groups in the array (e.g., 3 rows of 4 = 4 + 4 + 4 = 12).

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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.

2 + 2 =

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An array has equal rows and equal columns.

Repeated addition finds the total.

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.

2 + 2 = ___ — 4. 2 trays with 2 apples in each: skip-count the trays — 2, 4.

3 rows of 4 = 4 + 4 + 4 = 12

Let's count the stars in this picture. They're lined up in neat rows and columns — that's called an array.

First, let's count the rows going across. One, two, three. There are three rows.

Now let's count how many stars are in each row. One, two, three, four. Four stars in every row.

So we have three rows of four. We can say that as 'three rows of four.'

Instead of counting one by one, we can add. The first row has four stars. Write four.

The second row also has four. Add another four.

And the third row has four too. Add one more four.

Grade 2 · Counting an array of stars by rows

Now let's add them up. Four plus four is eight.

And eight plus four more is twelve.

Three rows of four equals twelve. Repeated addition helps us count arrays fast!

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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Standard

CCSS.2.OA.C.4

Use addition to find the total number of objects arranged in rectangular arrays with up to 5 rows and up to 5 columns

Grade 2

Quoted from the Common Core State Standards.

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A star here is the top of a twelve-rung ladder, in four blocks of equal length — three of facts and one of the skill used in a real question — where a right answer climbs one rung and a wrong one drops back to the start of the block, never below it. The star is kept for good. How we grade

All of Grade 2

This is one rung of 85 in Grade 2 mathematics, in the order they build on each other.

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