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Find b where 3723(base 10) = 123(base b).
Age
14 to 16
Challenge level
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Problem



Back to Basics

In March we posed the problem:

"The number $3723$ (in base $10$) is written as $123$ in another base.

What is that base?" ............ The answer to this can be found in the March problem archive.

We could have written this question as:



Find b where $3723_{10} = 123_{b}$

So, moving on ...................

$123_{20}$ is $1 \times 20^2 + 2 \times 20 + 3 = 443_{10}$

$123_{21}$ is $1 \times 21^2 + 2 \times 21 + 3 = 486_{10}$

$123_{22}$ is $1 \times 22^2 + 2 \times 22 + 3 = 531_{10}$

$531 - 486 = 45$

$486 - 443 = 43$

Investigate these differences when $123_{b}$ is converted to base $10$ (for different values of $b$).

Try to explain what is happening.