Before we start adding big numbers, let's nail down the most important building block.
Key Strategy: Bridge Through 10
When two single-digit numbers add up to more than 10, don't try to hold the whole thing in your head at once. Instead, complete to 10 first, then add what's left.
Example: What is 8 + 7?
First, figure out how much 8 needs to reach 10:
8 + 2 = 10
You "borrowed" 2 from the 7, so there are 5 left:
7 - 2 = 5
Now just add what's left to 10:
10 + 5 = 15
A Few More Examples
What is 6 + 7?
6 needs 4 to reach 10. That leaves 3 from the 7.
10 + 3 = 13
What is 9 + 6?
9 needs just 1 to reach 10. That leaves 5 from the 6.
10 + 5 = 15
What is 5 + 8?
5 needs 5 to reach 10. That leaves 3 from the 8.
10 + 3 = 13
Know Your Complements
To make this fast, memorize what each number needs to reach 10:
1 + 9, 2 + 8, 3 + 7, 4 + 6, 5 + 5
Once these pairs are automatic, bridging becomes effortless.
Practice, Practice, Practice
The exercise below only gives you problems that cross 10 — no easy ones like 3 + 4. Answer all 25, and try to make each one feel instant.
Once this is second nature, Strategy 1 will feel much easier!