Lesson Problems on simple interest accounts

Problems on simple interest accounts

Problem 1

Use the simple interest formula and write equation for the future value

    3000 = x*(1+0.06*2),


where x is the unknown starting deposit.


From this equation, find x

    x =  = 2678.58  (rounded to the closest greater cent).   ANSWER

Problem 2

Let x be original price.

The reduced cost after the deduct is  (x - 0.13x) rands.

So we write an equation

    x-0.13x = 4699.00


Simplify and find x

    0.87x = 4699.00

    x = 

    x = 5401.15.


ANSWER. The original price of the washing machine was R5401.15.

Problem 3

Let x be the investment at 13%.

Then the investment at 11% is )19000-x) dollars.


Write the total annual interest equation

    0.13x + 0.11*(19000-x) = 2290  dollars.


Simplify this equation and find x

    0.13x + 0.11*19000 - 0.11x = 2290

    0.13x - 0.11x = 2290 - 0.11*19000

        0.02x     =    200

            x     =    200/0.02 = 10000.


ANSWER.  $10,000 invested at 13% and the rest,  $19000 - $10000 = $9000 invested at 11%.


CHECK.   0.13*10000 + 0.11*9000 = 2290  dollars, the total annual interest.   ! correct !