Estimating Percent Mentally 10% 10% Lola borrowed $125 from a pawn shop. She’ll have to pay back the loan, plus the pawn shop charges an additional 9.9% fee. ≈ how much will her additional fee be? Step 1: Look at your cost and your percent. Do they need rounding? ~ ~ $125 is OK, but let’s round 9.9% to 10% 10% 1 space to the left Step 2: To find 10%, slide the decimal 1 space to the left. 5% ∞ do the 10% trick ∞c∞cut that number in half 15% o the 10% trick ∞c∞cut that number in half ∞a∞add both numbers 20% o the 10% trick ∞d∞double that number 25% o 20% + 5% or ∞m∞mentally divide the number by 4 50% ∞r∞round your number ∞c∞cut it in half 0 Fee is about $12 or $13.

Estimating Percent Mentally about $ $0.06 (5 or 6 cents) ≈$ $0.41 (about 40 or 41 cents) ≈ $ $7.40 ≈ $59 - $60 ≈ $ $1200 ≈ $1,6 00,000, $2,000,000,000 (1.6 trillion to 2 trillion) ≈ $1 - $1.20 (10%) ≈ $800 (10%) ≈ $60 + $30 = $90 (10%) + (5%) = (15%) = $.02 (2 cents) (25%) ≈ $16 4 ≈ $50,000 - $55,000 (50%) -->$0.08 = (10%) 2 ≈$.08 (or 8 cents) --> $1 2 ≈$0.08 (8 cents) 4 ≈$28,000 4 ≈ $7,000 (25%) ≈$100,000 2 ≈ $1,000,000 2 $ or $900,000 $.04 (or 4 cents) (5%) = $.50 - $.60 (5%) ≈ $ $20000 = $60,000 (10%) + (5%) = (15%) ≈ $.1 2 (10%) + $.06 + (5%) = $.15 - $.20 = (15%) ≈ $4 (10%) ● (2) = $8 = (20%) ≈ $50 00 (10%) ● (2) = $10,000 (20%) ≈ $ ● 2 = $40,000 - $50,000 (10%) ● 2 = (20%) ≈ $4 - $5 (25%) ≈ $500,000 - $550,000 (50%) ≈ $190 - $200 (50%) ≈$ > $800 2 = $400 (5%)

sales tax Tina bought a set of golf balls sells for $20 and the sales tax is 5.75% of the price. What is the total cost of the set? To find the sales tax,... Next, add the sales tax to the regular price. Answer: The total cost of the set of golf balls is $21.15 Sales Tax Sales Tax (20) (price)(tax rate) as a decimal 1.15 (sales tax) (reg price) $21.15 (total cost) Multiply Multiply the price and the tax rate (as a decimal) (.0575) 5.75% 5.75%.0575

tip tax Linda and Bob went to dinner, received lousy service, and decided to tip the server only 12%. If the prepared foods tax is 4.75%, and they ordered $68.19 of food and drinks, what will they pay? To find the tip,... Finally, add them up. Answer: Linda and Bob will pay $ Tip, then Tax (68.19) 8.18 (68.19) 3.24 (price) (tip rate) as a decimal Next, to find the tax Multiply Multiply the price and the tip rate (as a decimal). (price) (tax rate) Multiply Multiply the price and the tax rate. (.12) 12% 12% % 4.75%.0475 (.0475)

Mort and Teddy receive a “15% off” coupon for Bob’s Burgers. They order $22.57 of food and drinks, decide to tip 20%, and the food tax is 5 %. What will they pay in total? new price To find the tip, multiply the new price and the tip rate (as a decimal) Finally, add them up. They paid $24.07 Discount, then Tip, then Tax (19.18)(.20) = (19.18)(.055) = To find the discount,... (22.57)(.15) 3.39 Multiply the price and the discount rate (as a decimal) = = (price) (discount rate) as a decimal new price Now, subtract the discount from the old price to get the new price. new price To find the tax, multiply the new price and the tax rate (as a decimal)

DECIMAL …move the decimal 2 spaces to the right. Converting Between Decimal and Percents PERCENT From a to a 0.13=.13 13% = 0.9=.90= 90% = 0.27= 0.27% 0013= % = DECIMAL …move the decimal 2 spaces to the left. PERCENT From a to a 0.78 =78 78% = 0.05 = 5 5% = 1.75 = % = % =

To change a fraction to a percent, 1. Check the denominator = = 35% = ÷ ÷ 372 = 72% 72% 3 7 * Can it be changed to 100? 2. Rewrite the fraction with a denominator of 100. can’t What if the denominator can’t be changed to 100? a. Divide =3 ÷ … b.Change to a percent * slide the decimal 2 to the right d. Round to the nearest tenth. 42.9% c. Slap a percent sign on it. % yes 3. Write it as a percent.

To change a percent to a fraction, 1.Re-write the percent as a fraction over = 2. Simplify. 8% ÷ % ÷ 25 Converting Percents to Fractions 11 4 = % ÷ 4 9_ 250 = 36_ 1000 = *If there’s a decimal, move it to the end. … but, what you do to the numerator.. … you also do to the denominator 0

Modeling Fractions, Decimals & Percents.

Gene found a bank offering a certificate of deposit that pays 4% simple interest. He has $1,500 to invest. How much interest will he earn in 3 years? To find interest, use a formula Replace the variables: ~ P with $1,500 ~ R with.04 ~ T with 3. Multiply. Answer: Gene will earn $180 in interest in 3 years. Finding Interest INTEREST extra money someone pays when they borrow money. I = PRT I = I = 180 PRINCIPAL amount of money you borrow or lend.RATE written as a decimal interest rate written as a decimalTIME years of the loan Why.04? All % must be written as decimals. $ I = P R T

8.9% interest rate5 years$5,340interest principal Joan works for West Bank, and she just made a car loan at 8.9% interest rate for 5 years. The bank will earn $5,340 in interest. How much principal did she loan? 1. Replace the variables: ~ I with ~ P with p ~ R with.089 ~ T with 5. Finding Principal, Rate, or Time 5340= p I = P R T 5340= p ,000 = p Joan loaned $12,000 in principal. 2. Multiply (rate time) 3. Divide to find p. What interest rate Collette put $400 in principal in a savings account for 2 years, and she earned $7.20 in interest. What interest rate was she earning? Ralph just finished paying off a $3500 loan. He paid an additional $ in interest on his 19.9% loan. What was the length of time on this loan? I = P R T 7.2 = 400 R = 800 R = R The rate is 0.009, or 0.9% = T = T = T It was a 30 month loan. I = P R T