LESSON 6 Adding and Subtracting in Space

Rounding and Estimating

Mrs. Dewey’s class is learning about satellites. A satellite is an object that orbits around the Earth in outer space. The first artificial satellite, Sputnik I, was launched into orbit in 1957. Today, thousands of artificial satellites orbit the Earth. Many satellites send useful data back to Earth while others are no longer used and are considered “space debris.” The table below shows the number of satellites in orbit in 2008.

Grace wanted to estimate the total number of orbiting satellites that were launched by India and Japan. She decided to start by rounding the numbers for both countries.

Round numbers are often used when estimating because they are convenient to think about. We can make estimates by first rounding numbers to the nearest tens, hundreds, thousands, etc. A number line can help when you round a number.