Directions
Store discounts are often in multiples of 10 (20% or 50% off) and multiples of 5 (15% or 25% off).
20% of a number = (10% of the number) × 2
50% of a number = (10% of the number) × 5
Easy enough, right? Well, 5% is half of 10%.
So, 5% of a number = (10% of the number) ÷ 2
Here’s a sample problem:
A $30 clock is marked down 35%. What's the sale price?
Think: 35% = 30% + 5%
First: 10% of $30 is $3.
Then: 30% of $30 = (10% of $30) × 3 = ($3) × 3 = $9.00
So, 30% of $30 is $9.00
Next: 5% of $30 = (10% of $30) ÷ 2, so ($3) ÷ 2 = $1.50
So, 5% of $30 is $1.50
Now we have all we need to find 35% of $30.
35% of $30 = (30% of $30) + (5% of $30) = $9.00 + $1.50 = $10.50
The $30 clock is discounted $10.50. Subtract $10.50 from $30 to get the sale price: $19.50.