Mammoth Memory

% rate of interest

Example 1

Harriet had `£3500` in her savings account. After a year she had `£3800`. What `%` rate of interest did she have on her account?

Guide to find interest rates

Multiply both sides by `x` to get `x` on its own (what ever you do to one side you do to the other).

`(3500timesx)/3800=(100timescancelx)/cancelx` 

 

Multiply both sides by `3800` to get `x` on its own

  `(3500xtimescancel3800)/cancel3800=100times3800`

`3500x=100times3800` 

 

Divide both sides by `3500` to get `x` on its own

 `(cancel3500x)/cancel3500=(100times38cancel00)/(35cancel00)`

`x=(100times38)/35`

`x=108.57%` 

 

After a year Harriet had `108.57%` of her original amount of `£3500`. Take away the original amount which is represented by `100%` to find out the rate of interest.

 

`108.57 - 100 = 8.57%` per annum

 

Answer: Harriet had `8.57%` interest rate

 

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