Question

Reduce $7215$ from scale twelve to scale ten by working in scale ten, and verify the result by working in the scale twice.

Answer 1

In scale of ten
7215
12
---------
86
12
--------
1033
12
--------
12401
Thus the result is $12401$ in each case.
$7215$ in scale twelve means $7\times {12}^3+2\times {12}^2+1\times 12+5$ in scale ten. The calculation is most readily effected by writing this expression in the form $\left[\right(7\times 12+2)\times 12+1]\times 12+5$; thus we multiply $7$ by $412$ and add $2$ to the product; then we multiply $86$ by $12$ and add $1$ to product; then $1033$ by $12$ and add $5$ to product.