Percent

• Percent is parts per hundred.
• Alternative it is parts/whole * 100%
• It allows us to make comparisons.
  • I can borrow $102 from Bob, but I must repay him $123 in a year.
  • I can borrow $72 from Sue, but I must repay her $90 in a year.
  • Which should I take if I need $50?
  • Bob is charging (123-102) = $21 in interest
  • which is 21/102 x 100% = 20.59% interest
  • Sue is charging (90-72) = $18
  • Which is 18/72 * 100% = 25% interest
  • In some sense, Bob has a better interest rate.
• Some procedures:
  • Converting from a decimal to a percent:
    • Multiply by 100 %
  • Do problems 11 and 12 page 607
  • Converting from a percent to a decimal:
    • Divide by 100%
  • Do problems 15, 17 and 19 page 607
  • Converting from a fraction to a percent:
    • Convert the fraction to a decimal.
    • Convert the decimal to a percent.
  • Do problems 7,8,9 page 607
• Do problems 26 and 29 page 607
• Percent change
  • percent change = (new amount - old amount)/old amount * 100%
• Do 41, 42 page 608