A total amount of ₹7000 is deposited in three different saving bank accounts with annual interest rates of 5%, 8% and 
respectively. The total annual interest from these three accounts is ₹550. Equal amounts have been deposited in the 5% and 8% savings accounts. Find the amount deposited in each of the three accounts, with the help of matrices.
Let the deposited be x, y and z respectively.
As per the Data we get,
x + y + z = 7000
5%x + 8%y + 8.5%z = 550
i.e 5x + 8y + 8.5z = 55000
x – y = 0
These three equations can be written as
A X = B
|A| = 1(0 + 8.5) – 1(0 – 8.5) + 1(– 5 – 8)
= 1(8.5) – 1(– 8.5) + 1(– 13)
= 8.5 + 8.5 – 13
= 4
Hence, the unique solution given by x = A – 1B
C11 = (– 1)1 + 1 (0 + 8.5) = 8.5
C12 = (– 1)1 + 2 (0 – 8.5) = 8.5
C13 = (– 1)1 + 3 (– 5 – 8) = – 13
C21 = (– 1)2 + 1 (0 + 1) = – 1
C22 = (– 1)2 + 2 (0 – 1) = – 1
C23 = (– 1)2 + 3 (– 1 – 1 ) = 2
C31 = (– 1)3 + 1 (8.5 – 8) = 0.5
C32 = (– 1)3 + 2 (8.5 – 5) = – 3.5
C33 = (– 1)3 + 3 (8 – 5) = 3
Adj A = 
X = A – 1 B = 
X = 
X = 
X = 
= 
Hence, x = 1125, y = 1125 and z = 4750
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