Answer:
0.015625 left.
Explanation:
If we start with say 100g of the material, in 10 years there is 100 * 1/2 =
50g left ( = 0.5 left).
In 20 years there is 100*(1/2)^2 = 25 g left.
In n*10 years there is 100(1/2)^2 g
So in 60 years there is 100(1/2)^6 = 1.5625 g left
This is 1.5625 %
= 0.015625 of the origin material left.