the half life of another uranium isotope is 245000 yrs what %of the original material is left after 980000 yrs

Question

uranium isotope is 234 U
92

Answer 1

980000 years correspond to 980000/245000=4 periods

the formula of ramining atoms is

N=N0*2^(-t/T) here t/T=4

and N = N0*2^(-4) = N0/16 = 0.0625N0

0.0625= 6.25%

Answer 2

After 980000 years, 4 half lives have passed so:
After 1st half life = 1/2
After 2nd half life = 1/4
After 3rd half life = 1/8
After 4th half life = 1/16
1/16 = 6.25%

Answer 3

Is this a trick question? 12.5% left (half of half of half).