Doubles Facts (1+1 through 5+5) - First Grade Mathematics

Have you ever looked in a mirror and seen your exact reflection looking back at you? In mathematics, when you add a number to its exact twin, you create a doubles fact! Doubles facts are some of the most memorable and powerful equations in all of arithmetic. Once you know your doubles facts by heart, they become permanent mental anchors that help you solve many other addition and subtraction problems. In this chapter, you will master all the doubles facts from 1 + 1 through 5 + 5, connect them to real-world objects, and learn why every double always makes an even number.

The Core Doubles Facts from 1+1 to 5+5

A doubles fact has two identical addends.

The Core Doubles Facts within 10:

1 + 1 = 2     [*] + [*]                         = [**]
2 + 2 = 4     [**] + [**]                       = [****]
3 + 3 = 6     [***] + [***]                     = [******]
4 + 4 = 8     [****] + [****]                   = [********]
5 + 5 = 10    [*****] + [*****]                 = [**********]

Real-World Pictures for Every Double Fact

To help your brain remember each doubles fact instantly, connect each equation to an object you see in real life: 1 + 1 = 2: Two eyes on a face, or two shoes in a pair! 2 + 2 = 4: Four tires on a car, or four legs on a dog! 3 + 3 = 6: Six legs on an insect (3 on the left, 3 on the right), or a half-dozen egg carton with two rows of three! 4 + 4 = 8: Eight legs on an octopus or spider (4 on each side)! 5 + 5 = 10: Ten fingers on your two hands (5 on the left hand, 5 on the right hand)!

Why Doubles Always Equal Even Numbers

Every time you add a number to itself, you are creating pairs.

Doubles Always Make Pairs:
3 + 3 = 6:
  Top Row:    (*)  (*)  (*)
  Bottom Row: (*)  (*)  (*)
  Pairs:      pair pair pair -> 3 complete pairs, 0 leftovers!

No Leftovers

Because each item in the first group has an identical twin in the second group, every item can be paired up perfectly. That means the sum of any doubles fact is always an even number: 2, 4, 6, 8, 10! You will never get an odd number like 3, 5, 7, or 9 when you add two identical whole numbers.

Using Finger Doubles for Rapid Recall

Your hands are the ultimate tool for practicing doubles facts.

Finger Doubles Display:
Hold up 1 finger on each hand:  1 + 1 = 2
Hold up 2 fingers on each hand: 2 + 2 = 4
Hold up 3 fingers on each hand: 3 + 3 = 6
Hold up 4 fingers on each hand: 4 + 4 = 8
Hold up all 5 fingers on both:  5 + 5 = 10!

Flash and Say

Practice flashing matching fingers on both hands at the same time and shouting the answer: "Double 4 is 8! Double 3 is 6! Double 5 is 10!" Saying them aloud builds instant mental reflex.

Practice Exercises

Exercise 1: Write down all five doubles addition facts from 1 + 1 through 5 + 5 and their sums.

Exercise 2: An insect has 3 legs on its left side and 3 legs on its right side. What doubles fact shows how many legs the insect has in all?

Exercise 3: A spider has 4 legs on one side of its body and 4 legs on the other side. What is the sum of 4 + 4?

Exercise 4: Can a doubles fact ever have a sum of 7? Explain why or why not using what you know about pairs.

Solutions and Explanations

Solution to Exercise 1: The five doubles facts are: 1 + 1 = 2 2 + 2 = 4 3 + 3 = 6 4 + 4 = 8 5 + 5 = 10

Solution to Exercise 2: The doubles fact is 3 + 3 = 6. The insect has 6 legs in all.

Solution to Exercise 3: The sum of 4 + 4 is 8. A spider has 8 legs in all.

Solution to Exercise 4: No, a doubles fact can never have a sum of 7. Adding a whole number to itself always creates equal pairs, resulting in an even number. The number 7 is an odd number (it would leave 1 leftover item without a pair).