Half life worksheet answer key 3. what percent of a sample as-81 remains un-decayed after 43.2 seconds

The final mass after decay can be obtained by using under given relation:

half life period of As-81 = 33 seconds

mf = mi x (1/2^n)

= 100 x ( 1/2^(43.2/33))

= 40.4 %

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this