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Using Decimals, Fractions, Percentages and Ratios

Using Decimals, Fractions, Percentages and Ratios. To get a new value. When you are using decimals, percentages, fractions and ratios the main purpose is to get a new value. To get this new number we need to multiply. ×. Using Decimals.

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Using Decimals, Fractions, Percentages and Ratios

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  1. Using Decimals, Fractions, Percentages and Ratios

  2. To get a new value When you are using decimals, percentages, fractions and ratios the main purpose is to get a new value. To get this new number we need to multiply. ×

  3. Using Decimals Decimals are the easiest to use. Just multiply the decimal by the total. e.g. Find 0.55 of 300. 0.55 × 300 = 165 Find 0.04 of 50 0.04 × 50 = 2

  4. Using Fractions Fractions are almost as easy as decimals. You have two choices. 1. Use the fraction button on the calculator. 2. Change the fraction into a decimal by dividing the top by the bottom. Then solve the problem just like it was a decimal.

  5. e.g. Find ½ of 85. ½ × 85 = 42.5 or 1 ÷ 2 = 0.5 0.5 × 85 = 42.5

  6. Using Percentages First change them into a decimal by dividing by 100. Then solve by multiplying. e.g. What is 15% of 60? 15 ÷ 100 = 0.15 0.15 × 60 = 9

  7. Using Ratios First change the ratio into two fractions. The top number is one of the numbers in the ratio. The bottom number is the total. e.g. 4 : 5 4/9 and 5/9 are the two fractions 3 : 18 3/21 and 18/21 are the two fractions

  8. When you have the fractions you can solve the question by multiplying. You will two answers, one for each fraction. e.g. $600 is split between Frank and Emma in a ratio of 2 : 3. Fractions are 2/5 and 3/5 Frank 2/5 × 600 = $240 Emma 3/5 × 600 = $360

  9. Increasing When a question says to increase an amount by a decimal, fraction or percentage you do it in two steps. 1. Work out the percentage of. 2. Add the answer to the starting total.

  10. e.g. Your savings of $200 increase by 30%. How much do you have? 30 ÷ 100 = 0.3 200 × 0.3 = $60 200 + 60 = $260 A 6 metre tree grows by ¼. What is its new height? 6 × ¼ = 1.5m 6 + 1.5 = 7.5m

  11. Decreasing When a question says to decrease an amount by a decimal, fraction or percentage you do it in two steps. 1. Work out the percentage of. 2. Subtract the answer from the starting total. `

  12. e.g. The level of water in the pool decreases by ¾. The level starts at 1.2m 1.2 × ¾ = 0.9m 1.2 – 0.9 = 0.3m The shoes have a price-tag that reads $120. The store is having a 20% off sale. How much will the shoes cost? 20 ÷ 100 = 0.2 120 × 0.2 = $24 120 – 24 = $96

  13. Finding old values When you want a number from the past you have to work backwards. You must divide. Usually this is done to find out what a number used to be before that number was increased or decreased. e.g. GST is 15%. A car costs $23 000 after GST is added. How much does it cost without the GST?

  14. If something was increased Add 1 to the increase and divide the total by this number. e.g. GST is 15%. A car costs $23 000 after GST is added. How much does it cost without the GST? 15 ÷ 100 = 0.15 1 + 0.15 = 1.15 23 000 ÷ 1.15 = $20 000

  15. If something was decreased Take the decrease away from 1. Divide the total by this number. A leather jacket costs $150 during a 25% off sale. How much did it cost before the sale? 25 ÷ 100 = 0.25 1 – 0.25 = 0.75 150 ÷ 0.75 = $200

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