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Finding a percent of a number Textbook pages 434-440 January 14th, 15th, 16th Objective • I can find the percent of a quantity. • I can solve problems involving finding the whole, if given the part of the whole and percent Review Vocabulary • • • • • Is means Equal = Of means to multiply. Equations are going to be very important in this lesson. • Reminder, in order to solve equations you have to do the opposite. New Vocabulary • Interest: is the amount paid to use money. • Principal; the amount of money you borrow or save. • Annual interest rate: the amount of money you earn or pay per year Finding the percent of a Number • There are three ways to find the percent of a number. • Change the percent to a decimal then multiply. • Change the percent to a fraction then multiply. • By making a proportion. • Lets see what you find easier. • 50% of 8 • What way did you use? Try some more! • • • • • • • • Find 25% of 48 12, explain how you found your answer 10% of 85 8.5 45% 0f 20 9 60% of 60 36 Find the whole number given the part and percent • • • • • • 25% of what number is 8 Rewrite as an equation. .25 x n = 8 How do I solve? Divide both sides by .25 The answer is 32 Try some! • • • • • • 20% of what number is 30 150 40% of what number is 60 150 75% of what number is 54 72 Finding a discount • What is a discount? Give me an example • The discount is the amount that you will get off of the regular price. • Find the discount, (by finding the percent of the number) usually a percent off. • Then subtract from the original price, the answer you get is the sale price. Example • A pair of pants cost $36. The sale price is 25% off the regular price. What is the sale price? • 25% of $36 • What are we going to change 25% to. • 0.25 x $36 • $9 • Then subtract from the original price. • $36-$9 • $27 is he sale price of the pants Try some • • • • • A regular price for a shirt is $40. Find the sale price if the discount is 15%. $34 Find the sale price if the discount is 40% $24 Is there another way! • Can anyone think of another way to do these types of problem. • If you know that you will not have to pay the discount part, you will pay whatever percent is left. • If there is a 30% discount, that means you will pay 70% of the amount. This eliminates one step. Finding Sales Tax • Sales Tax is something extra you have to pay besides the price of something. • Anyone know what the sales tax is in Lorain county? • Find the sales tax the same way you find the percent of a number, then add that to the original number. Example • You are buying cat food for $9. The sales tax is 6%. What is the total of the purchase? • 6% x 9 • 0.06 x 9 • .54 cents • $9.00 + .54 = $9.54 Try One! • Cat toy is $8.00. The sales Tax is 6%. What is the cost. • $8.48 • You are buying a pair of shoes that cost $28.80. There is a 5% sales tax. What is the total amount of your purchase. • $30.24 Tips • A tip is added to the total of a bill. It is found the same way that you find the percent of a number. • Standard tipping amount is what? Simple Interest • Interest paid on only the principal. • Formula • SI=Principal x annual interest Rate x Time in years Percent of change • This can be either percent increase or percent decrease. • P%=amount of increase/original amount • • • • • P%=amount of decrease/original amount What is the percent change from 8 to 13? 62.5% What is the percent change from 60 to 12? 80% Try some. • A taco company puts 24 taco shells in every box. Recently the company expanded the box and put 25% more shells in each box. How many more shells are in each box? • 25% of 24 • .25 x 24 = 6 • 24 + 6 = 30 shells Finding the mark-up • A store that sells skateboards buys them from a manufacturer at a wholesale price of $57. The store’s mark-up is 150%. What is the retail price?