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Learn how to subtract integers with counters by transforming subtraction into addition and applying additive inverse principles using counters. Practice rewriting problems and solving word problems.
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How to subtract integers with counters • Rewrite the problem • Keep the first number the same • Change the problem from subtraction to addition • Make the last number its opposite • Lay out your counters to represent the problem. • Get rid of zero pairs • Count up what you have
Here’s how you rewrite the problem! -8 – 7 -8 + -7 7 changes to its opposite -7 -8 stays the same Subtraction becomes addition Additive Inverse Two integers that are opposite of each other are additive inverses. The sum of any number and its additive inverse is zero.
5 - -6 5 + +6 Now rewrite the problem. 5 positive units + 6 positive units Get rid of pairs. What do you have left? 11 positive units Answer = 11
-10 - -3 -10 + +3 Now rewrite the problem. 10 negative units + 3 positive units Get rid of pairs. What do you have left? 7 negative units Answer = -7
5 - 13 5 + -13 Now rewrite the problem. 5 positive units + 13 negative units Get rid of pairs. What do you have left? 8 negative units Answer = -8
You try & rewrite these problems Now follow adding rules or use algebra tiles to solve! Rewritten Problems • -4 – 8 = • 9 – 17 = • 3 - -5 = • 6 – 10 = • -8 - - 17 = -4 + -8 = 9 + -17 = 3 + 5 = 6 + -10 = -8 + 17 = -12 -8 8 -4 9
Solve these practice problems! • -5 - -4 = • 4 - -7 = • -12 – 4 = • 9 - -5 = • -5 - -9 = • -10 – 8 = • -4 - -4 = • -12 -3 = • -1 • 11 • -16 • 14 • 4 • -18 • 0 • -15
Word Problems • A submarine is situated at 450 feet below sea level and sinks 75 feet. What is the new position of the submarine? -450 – 75 = -525 feet The new position of the submarine was 525 feet below sea level. • The temperature at 8pm was 6°F. At 2am the temperature decreased 13 degrees. What was the temperature at 2am? 6 – 13 = -7°F The temperature at 2am was -7°F.