Rounding Tens and Hundreds
Key Terms: Rounding- Rounding involves either increasing or decreasing a number to the next digit. 56 would round to 60 Estimating- To find the sum or difference of numbers based on rounding 78+54 80+50=130 Approximate- To estimate a number, amount, or total by rounding it off to the nearest 10 or 100. About- Means to round then estimate the sum or difference.
Round 75 to the nearest ten. 80 70 71 72 73 74 75 76 77 78 79
75 rounds to 80 because 5 or more rounds to the next tens digit. 70 71 72 73 74 75 76 77 78 79
Round 34 to the nearest ten. 40 30 31 32 33 34 35 36 37 38 39
34 rounds to 30 because 4 or less keeps the same tens digit. 40 30 31 32 33 34 35 36 37 38 39
Round 27 to the nearest ten.
Does 27 round to 20 or 30? First find the number in the ones place 27 7 is greater than 5 so 27 rounds up to 30
Round 43 to the nearest ten.
First find the number in the ones place 43 Does 43 round to 40 or 50? 3 is less than 5 so 43 rounds down to 40
Round 236 to the nearest hundred.
First find the number in the tens place 236 Does 236 round to 200 or 300? 3 is less than 5, so round to 200
Round 476 to the nearest hundred.
First find the number in the tens place 476 Does 476 round to 400 or 500? 7 is more than 5, so round to 500
Round 333 to the nearest hundred.
Round 333 to the nearest hundred. Try it on your own. 300
Round 768 to the nearest hundred. Try it on your own. 800
Round 243 to the nearest ten. Try it on your own. 240
Round 67 to the nearest ten. Try it on your own. 70
Round 83 to the nearest ten. Try it on your own. 80
Compatible Numbers Compatible numbers are numbers that work well together. If a pair of numbers is easy to add or subtract, those numbers are compatible. This is NOT the same thing as rounding!
Compatible Numbers For example: 17+26 are NOT compatible numbers because they are no easily added. How can we make them compatible without changing the number too much? Change 17 to 15 Change 26 to 25 15+25=40
Let’s Practice! 27+56 What can you change these two numbers to in order to make them compatible and easy to add? REMEMBER: You don’t want to change the number too much, think about what is is closest to!
Let’s Practice! Change 27 to 25 Change 56 to 55 25+55=80
How can you change the following numbers to be compatible? 252-126 Your turn! How can you change the following numbers to be compatible? 252-126
Check your answer! 252-126 Change 252 to 250 Change 126 to 125 250-125= 125
Compatible Numbers Sally has 77 marbles in her jar and Ted has 54 marbles in his jar. Is it reasonable to say they have about 130 marbles together? EXPLAIN!
Compatible Numbers YES! It is reasonable to say they have about 130 marbles. Using compatible numbers you would change 77 to 75 and 54 to 55. 75+55= 130