(d) Let the principal be ₹ P and rate of interest be r.
Given, t = 2 yr
Amount = P
(1+)t = P
(1+)2Cl = Amount - Principal
= P
(1+)2 - P
According to the question,
P
(1+)2 - P = 5520
........(i)Again, principal = ₹ P, rate = r and time = 3 yr
SI =
=
According to the question,
= 7200 ⇒
=⇒ r =
∴ r =
.........(ii)On putting the value of r in Eq. (i). we have
P
(1+)2 - P = 5520
⇒ P
(1+)2 - P = 5520
⇒ P
[1+()2+] - P = 5520
⇒ P +
+ 4800 - P = 5520
⇒
= 55520 - 4800
⇒
= P
∴ P = 8000
On putting the value of P in Eq (ii), we get
r =
= 30
Therefore, rate of interest is 30% per annum.