Question

You drive 70 miles per hour but then slow your speed by 15 miles per hour. You then return to your speed of 70 miles per hour. Which expression shows how your speed changed?
-70 + 15 + (-15)
70 + (-15) + (-15)
70 + 15 + 15
70 + (-15) + 15

Answer 1

You first drive at 70 miles per hour, so your equation would start at +70. Then you decrease your speed by -15 meaning the next part of the equation is -15. So far we have 70 + (-15). Then you are speeding up by 15 once more meaning it is +15. Therefore, your expression is 70 + (-15)+ 15. Let me know if you have any other questions!

Answer 2

The correct answer would be d. 
70 mph is the original speed
when you add a negative number to a positive number, you are really subtracting the negative number from the positive. 70+(-15)=55
Then to return to your original speed you have to add the 15 back.
70+(-15)+15=70