Which of the numbers shown are odd? Which numbers are even?
55, 71, and 9 are odd; 34, 20, and 16 are even.
How can you tell whether a number is odd or even?
Possible answer: Even numbers can be divided into pairs. Odd numbers cannot be divided into pairs; there is always a number left over.
Add 16 + 55 using base-ten blocks. Explain your work.
The sum is 71. Possible explanation: I added the tens to the tens and the ones to the ones. There were more than 10 ones, so I traded to get 1 more ten. Then I had 7 tens and 1 one.
If you reverse the addends, is the sum still 71? Why or why not?
Yes. Possible explanation: You still have the same total number of tens and ones. It does not matter what order you write the numbers in.
Find the difference of 34 – 9 using a number line. Explain your work.
The difference is 25. Possible explanation: I hopped back by 10 to land on 24 and then hopped forward 1 to land on 25, which means I subtracted 9 in total.
If you switch the minuend and subtrahend, will the difference still be 25? Why or why not?
No. Possible explanation: You would start with fewer and subtract more. Your answer would be less than 0.
Choose any of the numbers. Multiply the number by 1. What is the result? Why?
The same number. One group of any number is the same as that number.
Choose any of the numbers. Multiply the number by zero. What is the result? Why?
The result is 0. Zero groups of any number is zero, and any number of groups of zero is zero.
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