1. Using Mental Math Subtraction

2. 2 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? Let’s use the method for rounding off. When using mental math, the goal is to make the numbers easy to use. In this problem let’s round the $ 17 off to $ 20.

3. 3 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? In this problem let’s round the $ 17 off to $ 20. $ 152 - $20 = ? The new problem becomes $152 - $20.

4. 4 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? $ 152 - $20 = $132 When we subtract $20 from $152 we get an answer of $132. But wait, there’s more!

5. 5 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? $ 152 - $20 = $132 The problem tells us only to subtract $17. We subtracted $20. Therefore, we subtracted too much. Since $20 is $3 more than $17, we need to adjust our answer and add $3 back to our answer. $ 132 + $3 = $135 The final cost of the jacket is $ 135.

6. 6 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? Again, we will use rounding numbers to make an easier problem. A Second Method for Subtacticon

7. 7 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? Let’s round the $17 off to $20. $ 152 - $17 = ? $ 152 - $20 = ? Now, we will add a new step.

8. 8 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? Let’s round the $17 off to $20. $ 152 - $17 = ? $ 152 - $20 = ? When we rounded the number 17 to 20, we needed to add 3 to it. Let’s add 3 to the 152 to keep the problem balanced.

9. 9 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? + 3 + 3 When we rounded the number 17 to 20, we needed to add 3 to it. Let’s add 3 to the 152 to keep the problem balanced.

10. 10 This jacket costs $152. It is on sale for $17 off. Using mental math, how much will this jacket cost? $ 152 - $17 = ? + 3 + 3 $ 155 - $20 = ? The new problem becomes $ 155 - $20. This is much easier to subtract in your head. $ 155 - $20 = $ 135. Since we balanced the numbers by adding 3, we don’t need to adjust our answer at the end.