Question

Compound Interest...
formula - a=p(1+r/100)n

question: $7800 is invested for 6 years at 9%pa

p=7800
r= 9
what is the 1 and n for?

Answer 1

The 1 was got when you brought the p outside the bracket, so originally in the first year you had Principal + rate(P+r), 2nd year (P + r)^2 etc., but you can bring the P outside the bracket to make P(1+r).

The n is ssimply the number of years it is invested for.

Answer 2

and it should be to the power of n in the above formula