Question

A bacteria population triples in number each day . if there are 2,551,500 bacteria on the 7th day , how many bacteria were present on the first day ?

Answer 1

Well it is triples you can tell that it is a division question.  So triples means by 3. 
The equation is 2,551,500 = d X 3^6. So, now 2,511,500 / 729 is your final answer, 3,500. Hope it helps :)

Answer 2

the total number of bacteria present on first day would be

2,551,500=x*3^6
x=2,551,500 / 3^6
=3,500