Ishita invested Rs. 1,20,000 a part of it at 10% per annum and the remaining at 12% simple interest . Her annual income from these investment is Rs. 12800 , find the amount invested in each case .

Given: 
Ishita invested Rs. 1,20,000 a part of it at 10% per annum and the remaining at 12% simple interest.

 Her annual income from these investment is Rs. 12800.

To do:  To find out the amount invested in each case.

Solution:
Let us assume  Rs.$x$ was invested at $10%$

So, Rs.$(12000−x)$ was invested @ $12%$.

In one year she will earn an interest=
$x\times10%+(12000−x)\times12%=1280$

⇒$12000\times12%−x\times2%=1280$

⇒$12000\times12−x\times2=128000$

⇒$2x=144000−128000=16000$

⇒$x=8000$

So, Rs.$8000$ was invested at $10%$

Rs.$(12000−8000)=Rs.4000$ was invested @$12%$.