Why does 9 x 10 = 90?

Because adding 9 10's together makes 90.

That is, because 101 + 102 + 103 + 104 + 105 + 106 + 107 + 108 + 109 = 90.

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Why does 9 x 10 = 90?

Because adding 9 10's together makes 90.

That is, because 101 + 102 + 103 + 104 + 105 + 106 + 107 + 108 + 109 = 90.

Keep practicing