Students join or separate in "chunks" or increments that make sense to them.
Combining Tens and Ones
652 - 128 = ?
600 - 100 = 500
50 - 20 = 30
2 - 8 = -6 (which means I still need to take 6 away)
500 + 30 - 6 = 524
Students deal with the different places (hundreds, tens, ones) and then combine them in the end.
Compensation
652 - 128 = ?
652 - 130 = 522
522 + 2 = 524
Students change or compensate a number to make it "friendly or easier" to work with. They then fix the answer in the end. (add or subtract the amount that was compensated.
Invented Strategies For Addition and Subtraction
Nicole 's class collected 652 cans for the recycling bin. On the way to the bin, 128 cans were lost. How many cans were put in the recycling bin?
Incremental
652 - 128 = ?652 - 100 ----> 552 - 10 ----> 542 - 10 ----> 532 - 2 ----> 530 - 6 ----> 524
128 + ? = 652
128 + 500 ----> 628 + 20 ----> 648 + 2 ----> 650 + 2 ----> 652
Students join or separate in "chunks" or increments that make sense to them.
Combining Tens and Ones
652 - 128 = ?600 - 100 = 500
50 - 20 = 30
2 - 8 = -6 (which means I still need to take 6 away)
500 + 30 - 6 = 524
Students deal with the different places (hundreds, tens, ones) and then combine them in the end.
Compensation
652 - 128 = ?652 - 130 = 522
522 + 2 = 524
Students change or compensate a number to make it "friendly or easier" to work with. They then fix the answer in the end. (add or subtract the amount that was compensated.
More Examples: