Draw a number line or model to solve each problem.

a. -9+15

b. -9-15

c. 9-15

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-9 -8-7-6-5-4-3-2-1 0 1 2 3 4 5 6

Explanation: for A

Start with the negative 9 and add 15

Do the same thing for b and c.

For b begin with -9 and go down to the left 15 more spaces you should wind up -24

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-24-23-22-21-20-19-18-17-16-15-14-13-12 etc

For c begin with positive 9 and subtract to the left 15 spaces

darwinism is survival of the fittest there for social darwinism is the survival of the wealthiest