Doubles and Near Doubles

Arithmetic · Axiom Academy

LESSON Doubles and Near Doubles The fastest addition facts — and how one double you know solves two more sums on either side of it. 1. A Double Is the Same Number, Twice Adding a number to itself gives a double . The two addends mirror each other — both sides are identical, so a double is really two equal groups counted together. 2. The Ten Doubles to Memorize These ten facts anchor everything that follows. Notice the pattern in the totals: each double is exactly 2 more than the one before it — 2, 4, 6, 8, 10, and on up. Going from one double to the next adds one to each side — one more on the left and one more on the right — so the total rises by 2 every step. That steady jump makes the doubles easy to rebuild if you ever forget one. 3. Near Doubles: A Double, Then One More When two numbers are one apart — like 6 + 7 — you don't need a new fact. Recall the double you already know, then adjust by 1. Inside 6 + 7 hides 6 + 6 = 12, and 7 is just one more than 6: There are two equally good routes, and they always land on the same sum — use whichever double comes to mind first: Double the smaller number, then add 1 7 + 8 = 7+7+1 = 15 Double the larger number, then subtract 1 7 + 8 = 8+8−1 = 15 Start from the double of the smaller number and step up one. 9 + 9 = 18, then subtract 1 → 17 Start from the double of the larger number and step back one. You've seen what makes a double, memorized the ten of them, and turned each one into the near double beside it.

This is the written version of the interactive lesson above. See the full Arithmetic course.