Answer:
after 6 half lives: 210(1/2)^6= 3.28125
Step-by-step explanation:
isotope to be reduced to half its initial mass at first:
210(1/2)=105 half it is original weight
after second life: 210(1/2)^2=105(1/2)=52.5
after third : 210(1/2)^3=52.5/2=26.25
after fourth : 26.25/2=12.125
after fifth : 13.125/2
Variable rate of change.
Plot the points and you'll see that the graph is not a straight line, therefore the rate of change is variable.
s=19
18s-17s+1=20
s+1=20
s=20-1
The answer is in the attachment,