Ans: 28%
The area of the larger circle is 25

π

^{2}

.
The area of the smallest circle is 9

π

^{2}

.
The area of the middle circle is 16

π

^{2}

.
Therefore the area of the ring is (16

π

- 9

π

) cm

^{2}

i.e. 7

π

^{2}

.
Therefore the percentage shaded is 28%.