Finding the Increase or Decrease percent
Let's understand how quantities change when expressed as percentages of the original amount. Here are some real-world examples:
(1) Student enrollment increased by 15 %
(2) Average temperature dropped by 8 %
(3) Company revenue needs to grow by 30 % this year.
There are two methods to solve percentage increase/decrease problems:
Method 1: Direct Calculation
A store manager wants to increase last month's sales of Rs. 5,000 by 25%. What is the target sales amount?
Step 1: Calculate the increase amount
25 % of Rs. 5,000 = (25/100) × Rs. 5,000 = Rs.
Step 2: Add to original amount
Target sales = Original + Increase = Rs. 5,000 + Rs. 1,250 = Rs.
Method 2: Unitary Method
The same problem using unitary method:
25 % increase means Rs. 100 becomes Rs.
So, multiply original amount by
Rs. 5,000 × (125/100) = Rs.
To summarise:
For increases: Final Amount = Original + (Original × Percentage/100)
For decreases: Final Amount = Original - (Original × Percentage/100)