Update README.md to fix typo error

Update README.md to fix typo error in the formula for calculating simple interest given principal, annual rate of interest and time period in years.

Author: patnaikn

README.md

@@ -10,7 +10,7 @@ Input:
    t, time period in years
    r, annual rate of interest
 Output
-   simple interest = p*t*r
+   simple interest = p*t*r/100
 ```
 
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