In planning her retirement, liza deposits some money at 3% interest, with twice as much deposited at 4%. find the amount deposited at each rate if the total annual interest income is $1320.

The principal amount deposited at 3 % is 12,000  and

The principal amount deposited at 4 $ is 2×12000 = 24,000

Step-by-step explanation:

Given as :

The total interest = $ 1320

The rate of interest are 3 %  and  4%

Time period = 1 year

Let the principal at  3 % =x

The principal at 4 % = twice x

I,e the principal at 4 % = 2 x

So , From simple interest method

Simple Interest =

So, =  

And =  

∵   +   = $ 1320

∴   + = 1320

Or, 3 x + 8 x = 1320 × 100

Or, 11 x = 132000

∴   x =

I.e  x = 12,000

So, The principal at 3 % is 12,000  and

The principal for 4 $ is 2×12000 = 24,000

Hence The principal amount deposited at 3 % is 12,000  and

The principal amount deposited at 4 $ is 2×12000 = 24,000  Answer

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.