Lesson 4, unit4 - Percent



Gr. 8 MathUnit 4 – PercentLesson 48.N.3 – Solving Percent Problems (Part 2)Lesson Focus:To solve percent increase and decrease problems. Increase or Decrease ProblemsThere are 2 ways to solve increase/decrease problems:Method 1Step 1 – Find the amount of the increase/decrease by multiplying the percent by the original amount. Be sure to turn the percent into a decimal before working with it! You do this by either dividing the percent by 100, or by moving the decimal 2 places to the left (to make the number smaller).Step 2 – Add the number calculated in step 1 to the original number if it is an increase problem.Subtract the number calculated in step 1 from the original number if it is a decrease problem.Method 2Increase Problem ex. a 30% increaseSince it is increased by 30%, the original number is now 100% + 30% = 130% of the original amount. Be sure to turn the percent into a decimal before working with it! Multiply the original number by 130% (1.3) to get your answer.Decrease Problem ex. a 30% decreaseSince it is decreased by 30%, the original number is now only 100% - 30% = 70% of the original amount.Be sure to turn the percent into a decimal before working with it! Multiply the original number by 70% (0.70) to get your answer.Ex. 1A length of 30 cm increased by 40%. What is the new length? Use each method to solveMethod 1:First find the amount of the increase, which is 40% of 30cm.0.40 x 30 = 12New length = old length + increase = 30 + 12 = 42 The new length is 42 cm.Method 2:The new length will be 140% of the original length.140% x 30 = 1.40 x 30 = 42The new length is 42 cm.Ex. 2A mass of 50 g decreased by 17%. What is the new mass? Use each method to solve.Method 1:First find the amount of the decrease, which is 17% of 50g.0.17 x 50 = 8.5New mass = old mass - decrease = 50 – 8.5 = 41.5 The new mass is 41.5 g.Method 2:The new mass will be 83% of the original mass.83% x 50 = 0.83 x 50 = 41.5The new mass is 41.5 g.Ex. 3You start an exercise plan that promises that you will lose 5% of your body weight in the first month and 8% in the second. If you weigh 150 pounds now, how much will you weigh in 2 months? Is this the same thing as losing 13% over 2 months? Explain.Month 1 – 150 x 0.05 = 7.5 lbs lost. You weigh 150 – 7.5 = 142.5 lbs after 1 month.Month 2 – 142.5 x 0.08 = 11.4 lbs lost. You weigh 142.5 – 11.4 = 131.1 lbs after 2 months.If you lost 13% over 2 months, you would lose: 150 x 0.13 = 19.5 lbs. You would weigh 150 – 19.5 = 130.5 lbs after 2 months.AssignmentDo #10, 12, 13ab - 18 p. 253Gr. 8 MathUnit 4 – PercentStudent CopyLesson 48.N.3 – Solving Percent Problems (Part 2)Lesson Focus:To solve percent increase and decrease problems. Increase or Decrease ProblemsThere are 2 ways to solve increase/decrease problems:Method 1Step 1 – Find the amount of the increase/decrease by multiplying the ____________ by the ____________ ___________. Be sure to turn the percent into a ___________ before working with it! You do this by either dividing the percent by _______, or by moving the decimal ___ places to the _____ (to make the number ____________).Step 2 – ___________ the number calculated in step 1 to the original number if it is an increase problem.____________ the number calculated in step 1 from the original number if it is a decrease problem.Method 2Increase Problem ex. a 30% increaseSince it is increased by 30%, the original number is now _____% + _____% = _____% of the original amount. Be sure to turn the percent into a ___________ before working with it! Multiply the original number by _____% (____) to get your answer.Decrease Problem ex. a 30% decreaseSince it is decreased by 30%, the original number is now only _____% - _____% = _____% of the original amount.Be sure to turn the percent into a ____________ before working with it! Multiply the original number by ____% (_____) to get your answer.Ex. 1A length of 30 cm increased by 40%. What is the new length? Use each method to solve.Method 1:Method 2:Ex. 2A mass of 50 g decreased by 17%. What is the new mass? Use each method to solve.Method 1:Method 2:Ex. 3You start an exercise plan that promises that you will lose 5% of your body weight in the first month and 8% in the second. If you weigh 150 pounds now, how much will you weigh in 2 months? Is this the same thing as losing 13% over 2 months? Explain.AssignmentDo #10, 12, 13ab - 18 p. 253 ................
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