In
how many years Rs 1000 double itself Solution Let P be the principal at any time t According to the given problem,
dp
dt  =
5
P
⎛100
⎞×
⎜
⎟
⎝
⎠
or
dp
dt  = P
20 (1)
separating the variables in equation (1), we get
P
dp  = 20
dt