Add awkward numbers by rounding, then adjusting
397 is nearly 400. Add 400 instead, take the 3 back off, and the hard sum turns easy.
- Spot a number close to a round one: in 289 + 397, 397 is 3 short of 400.
- Add the round number instead: 289 + 400 = 689.
- Take off the extra you added: 689 − 3 = 686.
Tip: Keep track of which way you rounded: round up, then subtract the difference.
Try it now: Do 46 + 98, 125 + 199 and $4.99 + $2.99. [144, 324 and $7.98.]
Next crumbs
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