Help...........in problems plzzz

1. the rate of disintegration is 10^17 atoms/second and half life is 1445 years. then number of atoms is
a. 1.44*10^ -17
b. 1.4*10^ 17
c. 6.57*10^ 27

2.a sample of radioactive material emits 1200 particles per second ad 200 seconds later. it is found that sample emits 150 particles per second the half life of material is
a. 100.8 sec
b. 75 sec
c. 66.66 sec
d. 25 sec


their answers are 1.c 2.c,,, but need their solutions cuz i dont kno how to solve them,,
d. not

By conversion, 1445 years = 4.56 × 10^10 seconds
Since, Rate of disintegration = Number of atoms / time
Then, Number of atoms = Rate of disintegration * time
Number of atoms = 10^17 * 4.56 * 10^10
Number of atoms = 4.56 * 10^27 atoms
(Check your options very well)