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- For each estimate below, tell whether the estimate is close enough. Explain your thinking for each.
- A carpenter is making a door. The opening for the door is 74 cm wide. The carpenter estimated the door should be about 70 cm wide.
- Keenya brings $30 to the store. She estimated that the groceries in her cart cost about $30. The actual cost is $32.49.
- Mr. Benson estimated there would be 300 players in a soccer league when he bought uniforms before the season started. There were 291 students that signed up for the league.
- Coach Salazar estimated there would be 20 players on her softball team when she bought uniforms before the season started. There were 11 players on her team.
It's About …
Jerome brought in an article with a number for the Newswire. Mrs. Dewey asked him to share the numbers he found. “My article says that 407,997 people visited the planetarium during 2006 and 458,156 people visited during 2007,” said Jerome.
“Can anyone estimate the total number of people who visited the planetarium during these two years?” asked Mrs. Dewey.
We often use round numbers in estimating because they are convenient. Round numbers such as tens, hundreds, or thousands end in zeros. They are one type of convenient number. A number line is helpful when rounding.
- Jerome estimated where 407,997 would be on the number line. He knew that it would be between 400,000 and 500,000 so he chose these two numbers as his benchmarks. Locate the mark Jerome made on the number line showing 407,997.
- Is 407,997 closer to 400,000 or 500,000?
- Round 407,997 to the nearest 100,000.
- Jerome used the same two benchmarks to estimate where 458,156 is on the number line. Find the mark Jerome made for 458,156.
- Is it closer to 400,000 or 500,000?
- Round 458,156 to the nearest 100,000.