Question

What is `9 xx 7 =`?

Answer 1

63

Answer 2

A bit of a cheat approach

Explanation:

To multiply by 10 is more straightforward but this will produce an error. This we can compensate for.

`9=(10-1)`

so `9xx7 color(white)("d") = (10-1)xx7`

`color(white)("d") (10xx7)-(1xx7)color(white)("ddd") =color(white)("ddd")70-7color(white)("ddd")=color(white)("ddd")63`