Mastering Percents for Shopping and Saving

Percents are a way to describe a part of a whole as "out of 100." They're essential for figuring out discounts at stores, tips at restaurants, and interest at banks.

Finding Percents

To find what percent one number is of another, use:

\[ \text{Percent} = \frac{\text{Part}}{\text{Whole}} \times 100 \]

Discounts and Markups

If an item costs \$50 and it's on sale for 20% off, calculate:

• \( 20% \) of \$50 is \( 0.20 \times 50 = \$10 \)
• Discounted price = \$50 - $10 = $40

Simple Interest

Banks use this formula for simple interest:

\[ I = P \times r \times t \]

where \( I \) = interest, \( P \) = principal (amount), \( r \) = rate (decimal), \( t \) = time (years).

• Saving \$200 at 3% for 2 years: \( I = 200 \times 0.03 \times 2 = \$12 \)