Decompose 9.949 and round to the nearest tenth and hundredth. Show your work on a number line. T: What decomposition of 9.949 best helps to round this number to the nearest tenth? S: The one using the most tenths to name the decimal fraction. I knew I would round to either 99 tenths or 100 tenths. I looked at the hundredths. Nine hundredths is past the midpoint, so I rounded to the next tenth, 100 tenths. One hundred tenths is the same as 10. T: Which digit made no difference when you rounded to the nearest tenth? Explain your thinking. S: The thousandths, because the hundredths decided which direction to round. As long as I had 5 hundredths, I was past the halfway point so I rounded to the next number. Repeat the process rounding to the nearest hundredth. Problem 3 A decimal number has 1 digit to the right of the decimal point. If we round this number to the nearest whole number, the result is 27. What are the maximum and minimum possible values of these two numbers? Use a number line to show your reasoning. Include the midpoint on the number line. T: (Draw a vertical number line with 3 points.) T: What do we know about the unknown number? S: It has a number in the tenths place, but nothing else past the decimal point. We know that is has been rounded to 27. T: (Write 27 at the bottom point on the number line and circle it.) Why did I place 27 as the lesser rounded value? S: We are looking for the largest number that will round down to 27. That number will be greater than 27, but less than the midpoint between 27 and 28. T: What is the midpoint between 27 and 28? S: 27.5 T: (Place 27.5 on the number line.) T: If we look at numbers that have exactly 1 digit to the right of the decimal point, what is the greatest one that will round down to 27? S: 27.4. If we go to 27.5, that would round up to 28. Repeat the same process to find the minimum value.
Decompose 9.949 and round to the nearest tenth and hundredth. Show your work on a number line. T: What decomposition of 9.949 best helps to round this number to the nearest tenth? S: The one using the most tenths to name the decimal fraction. I knew I would round to either 99 tenths or 100 tenths. I looked at the hundredths. Nine hundredths is past the midpoint, so I rounded to the next tenth, 100 tenths. One hundred tenths is the same as 10. T: Which digit made no difference when you rounded to the nearest tenth? Explain your thinking. S: The thousandths, because the hundredths decided which direction to round. As long as I had 5 hundredths, I was past the halfway point so I rounded to the next number. Repeat the process rounding to the nearest hundredth. Problem 3 A decimal number has 1 digit to the right of the decimal point. If we round this number to the nearest whole number, the result is 27. What are the maximum and minimum possible values of these two numbers? Use a number line to show your reasoning. Include the midpoint on the number line. T: (Draw a vertical number line with 3 points.) T: What do we know about the unknown number? S: It has a number in the tenths place, but nothing else past the decimal point. We know that is has been rounded to 27. T: (Write 27 at the bottom point on the number line and circle it.) Why did I place 27 as the lesser rounded value? S: We are looking for the largest number that will round down to 27. That number will be greater than 27, but less than the midpoint between 27 and 28. T: What is the midpoint between 27 and 28? S: 27.5 T: (Place 27.5 on the number line.) T: If we look at numbers that have exactly 1 digit to the right of the decimal point, what is the greatest one that will round down to 27? S: 27.4. If we go to 27.5, that would round up to 28. Repeat the same process to find the minimum value.