Skip Counting by 2s - First Grade Mathematics

Counting objects one by one is reliable, but as collections get larger, mathematicians use shortcuts to count much faster. One of the most popular shortcuts is skip counting. When you skip count by 2s, you hop over every other number, counting items in pairs. You use skip counting by 2s whenever you count pairs of shoes, pairs of mittens, eyes on faces, or wheels on bicycles. In this chapter, you will learn the rhythm of skip counting by 2s up to 20 and beyond, discover the pattern of even numbers, and practice grouping items into pairs.

Hopping Along the Number Line by 2s

Imagine a friendly grasshopper hopping along a number line, skipping over one number with every leap.

Hopping by 2s on the Number Line:
      +2          +2          +2          +2          +2
   /-------\   /-------\   /-------\   /-------\   /-------\
(0)   1   (2)   3   (4)   5   (6)   7   (8)   9   (10)

The Whispering Strategy

A wonderful way to learn the rhythm of skip counting by 2s is to whisper the skipped odd numbers and shout the even numbers: "(one) TWO! (three) FOUR! (five) SIX! (seven) EIGHT! (nine) TEN!" This rhythm helps your brain internalize the pattern.

The Sequence of 2s to 20

The sequence of counting by 2s is: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20. Every number in this sequence is called an even number.

The Secret Pattern of Even Endings

No matter how large an even number gets, its ones digit always ends with one of five magic digits.

The Five Even Endings:
Numbers ending in: 0, 2, 4, 6, or 8

Look at the 2s pattern continuing:
   2,  4,  6,  8, 10
  12, 14, 16, 18, 20
  22, 24, 26, 28, 30

Why They Are Called Even

These numbers are called even because any even quantity can be split into two equal teams with no leftover items. If you have 6 cookies, you can share them between two friends so each friend gets 3 cookies, and no cookie is left over.

Counting Real-World Pairs

Skip counting by 2s is the fastest way to count items that come naturally in pairs.

Counting 4 Pairs of Shoes:
 Pair 1:   (Shoe)(Shoe)  -> Count: 2
 Pair 2:   (Shoe)(Shoe)  -> Count: 4
 Pair 3:   (Shoe)(Shoe)  -> Count: 6
 Pair 4:   (Shoe)(Shoe)  -> Count: 8
Total: 4 pairs = 8 shoes in all!

Pairs vs. Total Items

Notice the difference between counting pairs and counting individual items: 4 pairs of shoes equals 8 single shoes. Each pair contains two units.

Practice Exercises

Exercise 1: Recite and write down the sequence of skip counting by 2s from 2 up to 20.

Exercise 2: Fill in the missing numbers in this skip counting sequence: 4, 6, , 10, , 14, 16, __, 20.

Exercise 3: You see 5 bicycles parked outside. Each bicycle has 2 wheels. Use skip counting by 2s to find the total number of wheels.

Exercise 4: Look at the numbers 14, 17, and 18. Which of these numbers is NOT part of the skip counting by 2s pattern, and how do you know?

Solutions and Explanations

Solution to Exercise 1: The sequence of skip counting by 2s from 2 to 20 is: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.

Solution to Exercise 2: The missing numbers are 8, 12, and 18. The complete sequence is 4, 6, 8, 10, 12, 14, 16, 18, 20.

Solution to Exercise 3: Count the wheels on the 5 bicycles by 2s: 2, 4, 6, 8, 10. There are 10 wheels in total.

Solution to Exercise 4: The number 17 is not part of the pattern. Numbers in the skip counting by 2s sequence are even and must end in 0, 2, 4, 6, or 8. The number 17 ends in 7, which makes it an odd number.