15. (3 1/2 − 2 2/3) : 2 1/4

\(3\frac12−2\frac23=\frac72−\frac83=\frac{21−16}{6}=\frac56\).

\(\frac56:2\frac14=\frac56:\frac94=\frac56·\frac49=\frac{10}{27}\).

Ответ: \(\frac{10}{27}\).