The interest you earn by intially investing some money is called as Simple interest.
If Principal = P, Rate = R% per annum, Time = T years, then
Simple Interest (S.I) = P * T * R / 100
P = 100 x S.I.
R = 100 x S.I.
and T = 100 x S.I.
Amount (A) = Principal(P) + Interest(I)
We can correlate it as
A = P + P * T * R/100
Or,
A = P(1 + T * R/100)
When type of interest is not specified, it is assumed to be simple interest.