Page 868 - Algebra 1

Estimation Strategies
Skills Bank Lesson 8
To estimate is to find an approximate answer. Rounding numbers is one way to estimate.
Rounding Rules
If the digit to the right of the Round 35_,679 to the nearest thousand. rounding digit is > 5, round up. 35,679 rounds up to 36,000.
If the digit to the right of the Round 35_,479 to the nearest thousand. rounding digit is < 5, round down. 35,479 rounds down to 35,000.
If the digit to the right of the Round 35_,579 to the nearest thousand. rounding digit = 5, then round up. 35,579 rounds up to 36,000.
Compatible numbers are numbers that are close in value to the actual numbers and are easy to add, subtract, multiply, or divide. Compatible numbers can be used to estimate. An overestimation is an estimate greater than the exact answer. An underestimation is an estimate less than the exact answer.
Estimate by Rounding
a. Sally has $23 to buy two shirts. One shirt is $9.75, and the other shirt is $10.95. Explain whether Sally should overestimate or underestimate the total cost. Then estimate the total cost and tell whether Sally has enough money to buy both shirts.
SOLUTION Sally should overestimate. If her estimate is more than the actual cost, then she has enough money to buy both shirts.
$9.75 + $10.95 To overestimate, round each number up. $10.00 + $11.00 = $21.00
The actual cost will be less than $23.00, so Sally has enough money.
b. Alan plans to drive 575 miles to his aunt’s house. He can drive 65 mi/hr. About how long will the trip take?
SOLUTION Alan should underestimate his speed.
Round 575 up to 600. Round 65 mi/hr down to 60.
600 ÷ 60 = 10 Distance divided by rate is equal to time. It will take Alan about 10 hours to drive to his aunt’s house.
Skills Bank Practice
a. Rico has $30 to buy school supplies. He wants to buy 2 packages of pens for $2.75 each, a backpack for $12.50, and 4 notebooks for $1.99 each. Tell whether Rico should overestimate or underestimate the total cost. Then estimate the total and tell whether Rico has enough money.
b. Jordan drives 120 miles. If his car gets 32 miles per gallon of gas, about how much gas will he use?
Example
1
Skills Bank 853
SKILLS BANK