Shop prices and GST

Parts and wholes The whole represents 100%. A part represents its stated share of that whole. Writing the share as a decimal makes one relationship work in both directions. part=share x whole. Multiply when you know the whole. Divide by the nonzero share when you know the part. If you are given the percentage for the rest, subtract it from 100% first. Example 30% of a school’s 90 music stands are being repaired. The number being repaired is 0.30 x 90=27. If you are told only that 27 stands are 30% of the stock, recover the stock with 27 0.30=90. Check by multiplying your recovered whole by 0.30. Dividing by 30 would give the wrong scale because 30% equals 0.30.

The whole represents 100%. A part represents its stated share of that whole. Writing the share as a decimal makes one relationship work in both directions.

\(\text{part}=\text{share}\times\text{whole}\).

Multiply when you know the whole. Divide by the nonzero share when you know the part. If you are given the percentage for the rest, subtract it from 100% first.

30% of a school’s 90 music stands are being repaired. The number being repaired is \(0.30\times90=27\). If you are told only that 27 stands are 30% of the stock, recover the stock with \(27\div0.30=90\).

Check by multiplying your recovered whole by 0.30. Dividing by 30 would give the wrong scale because 30% equals 0.30.