Question

What are divisibility rules useful for?

Answer 1

This is useful in factoring large numbers. There constant and diverse use also sharpens calculation / arithmetic skills.

Explanation:

Divisibility rules enable one to identify whether a number is divisible by another smaller number or not by examining digits and /or small operations on them but without attempting actual division or calculation.

This is useful in many ways such as factoring large numbers, also determining whether numbers are prime or composite.

There constant and diverse use also sharpens calculation / arithmetic skills and in fact enables one to identify other patterns too.

For example, in a number such as `XY25`, if `XY` is a product of two consecutive numbers say `XY=A(A+1)`, then `sqrt(XY25)=A5`. An example is `sqrt2025=45` as `20=4xx5`.