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Mental Mathematics Addition(+) & Subtraction(-)

Mental Mathematics Addition(+) & Subtraction(-). Tim Niemela Northern Michigan University. Mental mathematics is the process of producing an answer to a computation without using computational aids, for example calculators.

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Mental Mathematics Addition(+) & Subtraction(-)

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  1. Mental MathematicsAddition(+) & Subtraction(-) Tim Niemela Northern Michigan University

  2. Mental mathematics is the process of producing an answer to a computation without using computational aids, for example calculators. Mental mathematics makes use of a variety of strategies and properties. Next we consider several of the most common strategies for performing addition and subtraction of whole numbers mentally.

  3. Adding from the left (+) 67 60+30=90 (add the tens) +36 7+6=13 (add the units) 90+13=103 (add the two sums) 36 30+30=60 (double 30) +36 6+6=12 (double 6) 60+12=72 (add the doubles)

  4. Breaking up and Bridging (+) 67 67+30=97 (add the first number to the tens in the second number) +36 97+6=103 (add this sum to the units in the second number) 88 88+70=158 (add the first number to the tens in the second number) +77 158+7=165 (add this sum to the units in the second number)

  5. Trading off (+) 88 88+2=90 (add 2 to make a multiple of 10) +26 26-2=24 (subtract 2 to compensate for the 2 that was added) 90+24=114 (add the two numbers) 67 67+20=87 (add 20(the next multiple of 10 greater than 18)) +18 87-2=85 (subtract 2 to compensate for the extra 2 that was added)

  6. Using compatible numbers (+) compatible numbers are numbers whose sums are easy to calculate mentally 140 80 60 50 220 +150 140+60=200 80+220=300 50+150=200 200+300+200=700 200 300 200

  7. Breaking up and bridging (-) 97 97-40=57 (subtract the tens in the second number from the first number) -46 57-6=51 (subtract the units in the second number from the difference) 88 88-50=38 (subtract the tens in the second number from the first number) -55 38-5=33 (subtract the units in the second number from the difference)

  8. Trading off (-) 84 (84+4)=88; (36+4)=40 -36 (88-40)=48 (Add 4 to both numbers. Perform the subtraction, which is easier than the original problem.) 92 (92+6)=98; (24+6)=30 -24 (98-30)=68 (Add 6 to both numbers. Perform the subtraction, which is easier than the original problem.)

  9. Try It Yourself Mental Math Worksheet Worksheet Answers Mental Math JAVA application (Scroll to the middle of the page for the activity)

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