Question

What is `26 * 17`?

Answer 1

`26*17 = 442`

Explanation:

If I was trying to calculate this in my head, then I would probably choose to do it as follows:

`26 = 2 xx 13`

So we are looking for `2 xx 13 xx 17`

Then:

`13 xx 17 = (15 - 2)(15 + 2) = 15^2 - 2^2 = 225 - 4 = 221`

So:

`26 xx 17 = 2 xx 221 = 442`

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Another way would be to know that `3 xx 17 = 51`, so `6 xx 17 = 102`

Then:

`20 xx 17 = 10 xx 2 xx 17 = 10 xx 34 = 340`

So:

`26 xx 17 = (20 + 6) xx 17 = (20 xx 17) + (6 xx 17) = 340 + 102 = 442`