A type of bacteria in a Petri dish doulbles every hour. If there were 1,073,741,824 bacteria after 24 hours, how many were there to start with?

It multiply in a Geometric Progression

1st Term=a=?

common ratio = r = 2

last term=l = 1073741824

no. of terms in GP = 25

1073741824 = a*r^n-1

1073741824 = 2^24 * a

a = 1073741824 / 2^24

a=64 bacteria