Question

why do we need multiples and submultiples for measuring mass and time?

Answer 1

as some distance and time can be measured in metre or second means in their Si units but to make it easier we have multiples and submultiples..

they help us to understand them easily..

Answer 2

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The purpose of these multiples is to help us be able to express and easily understand large measured values. In a similar way, the submultiples are designed to help us be able to easily express and understand small measured values.