clc 
// Given that
t = 2 // life period of radioactive substance in years
T = 4 // time in years
m = 10 // mass of substance in mg
// Sample Problem 12 on page no. 12.35
printf("\n # PROBLEM 12 # \n")
printf("Standard formula used \n")
printf(" N = N_0/2^(n) ...... fraction after n half lives.\n")
N = m / T // in mg
printf("\n  Substance remained unchanged after 4 years is %f mg.",N)