Pre-Algebra 8-5 Estimating with Percents Warm-up

Pre-Algebra 8-5 Estimating with Percents Learn to estimate with percents.

Pre-Algebra 8-5 Estimating with Percents Going to get into groups of 3 Work together on wkbk pg. 68 #1-5 Come up with a strategy for estimating Each group will share their strategy for the problem I choose for them. You will have about 20 minutes.

Pre-Algebra 8-5 Estimating with Percents Some problems require only an estimate. Estimates involving percents and fractions can be found by using compatible numbers, numbers that go well together because they have common factors  compatible not compatible

Pre-Algebra 8-5 Estimating with Percents Estimate. A. 21% of 66 Instead of computing the exact answer of 21%  66, estimate. 21% =  Use compatible numbers, 20 and 100.  1 5 Simplify. 66  65Use compatible numbers, 65 and  65 = 13 Use mental math: 65 ÷ 5. So 21% of 66 is about 13.

Pre-Algebra 8-5 Estimating with Percents Estimate. B. 36% of 120 Instead of computing the exact answer of 36%  120, estimate. 36%  35%Round.  30% + 5%Break down the percent into smaller parts.  3  10% + 5% 35%  120 = (3  10% + 5%)  120 Set up an equation.

Pre-Algebra 8-5 Estimating with Percents Additional Example 1B Continued = % of 120 is 12, so 5% of 120 is 6. = 42 So 36% of 120 is about 42. = 3  10%  %  120 Use Distributive Property.

Pre-Algebra 8-5 Estimating with Percents Estimate. A. 29% of 86 Try This: Example 1A Instead of computing the exact answer of 29%  86, estimate. 29% =  Use compatible numbers, 30 and 100.  3 10 Simplify. 86  90 Use compatible numbers, 90 and  90 = 27 Use mental math: 90 ÷ 10. So 29% of 86 is about 27.

Pre-Algebra 8-5 Estimating with Percents Estimate. B. 44% of 130 Instead of computing the exact answer of 44%  130, estimate. 44%  45%Round.  40% + 5%Break down the percent into smaller parts.  4  10% + 5% 45%  130 = (4  10% + 5%)  130 Set up an equation. Try This: Example 1B

Pre-Algebra 8-5 Estimating with Percents = % of 130 is 13, so 5% of 130 is 6.5. = 48.5 So 44% of 130 is about = 4  10%  %  130 Setup an equation. Try This: Example 1B Continued

Pre-Algebra 8-5 Estimating with Percents The diameter of the Moon is about 2160 miles. If the diameter of the Moon is about 27% of the diameter of Earth, what is the approximate diameter of Earth?

Pre-Algebra 8-5 Estimating with Percents Additional Example 2 Continued 1 Understand the Problem The answer is the approximate diameter of Earth. List the important information: The diameter of the Moon is about 2160 miles. The diameter of the Moon is about 27% of the diameter of the Earth. Let e represent the diameter of the Earth  27%  e Diameter of the Moon  27%  Diameter of Earth

Pre-Algebra 8-5 Estimating with Percents Use compatible numbers: 2160 is close to 2000; 27% is close to 25% 2 Make a Plan Think: The numbers 2160 and 27% are difficult to work with. Find an equivalent ratio for 25%. 25% = =

Pre-Algebra 8-5 Estimating with Percents Solve 3 Think: 2000 is of what number?  2000 = e 8000 = e The diameter of Earth is approximately 8000 miles. Additional Example 2 Continued

Pre-Algebra 8-5 Estimating with Percents Look Back4 25% of 8000 mi is, or 2000 mi. This is the approximate diameter of the moon

Pre-Algebra 8-5 Estimating with Percents Lesson Quiz Estimate % of out of % of out of According to the last census, 33,871,648 people live in California, and 3,694,820 of those people live in Los Angeles. Estimate the percent of Californians who live in Los Angeles. 20% % 10% Possible answers: