Given:
log10 a = b
(10)b = a ......(1 mark)
Now,
102b-3 = (10)2b / (10)3
= (10b)2 / (10 × 10 × 10) .......(1 mark)
Substitute the value of (10)b = a, we get
= a2/1000 ........(1 mark)