Doubles Strategy

Another powerful shortcut is the doubles strategy. If you know that 35 + 35 = 70, then 35 + 37 is just 70 + 2 = 72. Your brain memorizes doubles faster than random sums, so building from them feels effortless.

This shines with near-doubles in everyday life. Splitting a $48 bill two ways is just half of a double: each share is exactly $24. Doubling is so instinctive that children grasp it before formal addition, and you can lean on that built-in skill to crack harder problems faster.