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Using Mental Math

Using Mental Math. Addition. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. Let ’ s use the breaking apart a number method. ?. 157. 38. Let ’ s review the picture above.

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Using Mental Math

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  1. Using Mental Math Addition

  2. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. • Let’s use the breaking apart a number method. ? 157 38 • Let’s review the picture above. • The line across the top with the “?” represents the number in all. • The 157 tells us how many pencils were sold last week. • The 38 tells us how many pencils were sold last week.

  3. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. ? 157 38 When we use the breaking apart a number method, we want to make the numbers easier to add. Numbers that have zeros do make adding easier because of the Identity Proper. (Any number plus zero is that number.) When I look at this picture, I would like to change the 157 to 160. To do this, I have to move 3 pencils from the 38 to the 157 to make the number 160.

  4. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. ? ? When I look at this picture, I would like to change the 157 to 160. To do this, I have to break apart the 38 by moving 3 pencils from the 38 to the 157 to make the number 160. 157 157 38 38 ? 157 3 35

  5. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. ? 157 38 Now that we have finished breaking apart the 38 into 3 plus 35, we can now add the 3 to the 157. ? ? 160 35 157 3 35

  6. The school store sold 157 pencils last week and 38 pencils this week. Use mental math to find how many pencils were sold in all. ? 157 38 Using mental math, it is much easier to add 160 plus 35. The answer is 195. ? 160 35

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