Mental Math and Rounding
Two classes sold 126 and 325 raffle tickets. Zane was adding the two amounts mentally. Make a ten or hundred to add mentally.
126 + 325 =
121 + 330 = 541
Which of the following sums will need to regroup ones as tens?
A. 156 + 130 C. 8,974 + 1,007
B. 198 + 21 D. 3,525 + 805
C and D
If you are saving up your money to buy a new game, would it be best to find an estimate or the exact amount of the money you have?
Exact amount
Stand up, do 5 jumping jacks.
Sit back down.
Use the associative property to fill in the missing numbers:
4 + (7 + 3) = ( + 7) +
( + 6) + = 8 + ( + 11)
4 + (7 + 3) = (4+ 7) +3
(8 + 6) +11 = 8 + (6 + 11)
Break apart the addends to add mentally.
128 + 343 =
100 + 20 + 8
300 + 40 + 3
400 + 60 + 11 = 471
Timothy bought one apple that weighed 234 grams, and two bananas that weighed 175 grams each. How much did his fruit weigh altogether?
584 grams
53 > 50
50+50+50+50+50=250
About 250 square feet of wood.
Get a drink of water. Then come back and sit down.
Refreshed!
Use the Commutative Property to find the missing number sentences:
17 + 19 = 95 + 25 =
___________ ____________
17 + 19 = 36 95 + 25 = 120
19 + 17 = 36 25 + 95 = 120
Round each addend to the indicated place value, then solve.
4,539 + 712, hundreds
4,500 + 700 = 5,200
$167 + $847
$1,014
Round each addend to its greatest place value to find an estimate.
3,492 + 2,857 =
3,000 + 3,000 = 6,000
Write an addition problem using 3 or 4 digit numbers and have someone next to you solve it.
Check that they answered your problem correctly.
This Property of Addition states that when you add zero to any number, the number remains the same.
Identity Property
Round each addend to the indicated place value, then solve.
56,038 + 10,271, tens
56,040 + 10,270 = 66,310
Trina has collected 1,002 baseball cards. Ashton has collected 4,609 baseball cards. About how many baseball cards do they have altogther?
Estimate:5,600-6,000
Exact: 5,611
How can you find the most exact estimate?
Round to the smallest place value.
There are a certain number of gumballs in a container. Use the three clues to figure out your estimate for how many gumballs there are.
1. There are between 700 and 800 gumballs.
2. If you add the number of gumballs and 7, the sum will end in 0.
3. The sum of all the digits is 15.
753 gumballs
This property states that the order in which you add numbers, does not change the sum.
The Commutative Property.
Use a mental math strategy (break apart or make a 10 or 100) to solve.
963 + 846 =
Methods may vary.
1,809
Yon is working on earning bitcoin by doing chores around his house and neighborhood. He earned 1,319 bitcoin his first year, 994 bitcoin his second year, and 2,055 bitcoin this year. So far, how much has Yon earned?
4,368 bitcoin
Determine whether each solution is reasonable. Use estimation to explain your thinking.
154 + 28 = 434
408 + 91 = 499
No, 150 + 30 = 180 which is not close to 434.
Yes, 410 + 90 = 500 which is close to 499.
Draw a picture on your board for 30 seconds. Go!
Artists!
This property states that the way in which addends are grouped, does not change the sum.
The Associative Property.