Mental Math

lessonbunny.com

Answer Key & Explanations

Mental Math · Grade 3 · Worksheet 2

1. Liam is organizing his baseball card collection. He has 8 pages in his binder and can fit 9 cards on each page. How many baseball cards can Liam fit in his binder in total? Answer: 72 Solution: Liam has 8 pages in his binder. Each page can hold 9 cards. We need to find the total number of cards that can fit in the binder.
   Full step-by-step solution

   Let's go step by step. Step 1: Understand the problem. Liam has 8 pages in his binder. Each page can hold 9 cards. We need to find the total number of cards that can fit in the binder. Step 2: Think about the operation. If 1 page holds 9 cards, then 8 pages hold: 8 × 9 cards. Step 3: Perform the multiplication. 8 × 9 = 72. Step 4: Interpret the result. The total number of baseball cards Liam can fit in his binder is 72. Final answer: 72

2. Lily is planting flowers in her garden. She has 84 flower seeds and wants to plant them equally in 7 different flower beds. How many seeds should Lily plant in each flower bed? Answer: 12 Solution: Lily has 84 seeds total and 7 flower beds. To find how many seeds go in each bed, divide the total seeds by the number of beds: 84 ÷ 7 7 × 12 = 84, so 84 ÷ 7 = 12 Therefore, Lily should plant 12 seeds in each flower bed.
   Full step-by-step solution

   Step 1: Lily has 84 seeds total and 7 flower beds. Step 2: To find how many seeds go in each bed, divide the total seeds by the number of beds: 84 ÷ 7 Step 3: 7 × 12 = 84, so 84 ÷ 7 = 12 Step 4: Therefore, Lily should plant 12 seeds in each flower bed. The answer is 12.

3. 401 - 196 = ? Answer: 205 Solution: Round 196 up to 200. Step 2: Subtract 401 - 200 = 201. Step 3: Since we subtracted 4 extra (200 - 196 = 4), add 4 back to the result.
   Full step-by-step solution

   Step 1: Round 196 up to 200. Step 2: Subtract 401 - 200 = 201. Step 3: Since we subtracted 4 extra (200 - 196 = 4), add 4 back to the result. Step 4: 201 + 4 = 205. The answer is 205.

4. A rectangular swimming pool is drawn on a grid. The pool is 15 meters long and 8 meters wide. What is the total distance around the outside edge of the pool? Answer: 46 meters Solution: The distance around a rectangle is called the perimeter. The formula for perimeter of a rectangle is: Perimeter = 2 × (length + width) Substitute the given measurements: Perimeter = 2 × (15 + 8) Add inside the parentheses: 15 + 8 = 23 Multiply by 2: 2 × 23 = 46 Include the unit: 46 meters The…
   Full step-by-step solution

   Step 1: The distance around a rectangle is called the perimeter. Step 2: The formula for perimeter of a rectangle is: Perimeter = 2 × (length + width) Step 3: Substitute the given measurements: Perimeter = 2 × (15 + 8) Step 4: Add inside the parentheses: 15 + 8 = 23 Step 5: Multiply by 2: 2 × 23 = 46 Step 6: Include the unit: 46 meters The total distance around the pool is 46 meters.

5. Liam is collecting trading cards. He has 48 cards in his collection. For his birthday, his friend Noah gives him a pack with 25 new cards. How many trading cards does Liam have now? Answer: 73 Solution: Liam starts with 48 trading cards. He receives 25 new cards from Noah. To find the total number of cards he has now, we add the new cards to the original number of cards.
   Full step-by-step solution

   Liam starts with 48 trading cards. He receives 25 new cards from Noah. To find the total number of cards he has now, we add the new cards to the original number of cards. Step 1: Write the addition problem. 48 + 25 Step 2: Add the ones place: 8 + 5 = 13. Write down 3 in the ones place and carry over 1 to the tens place. Step 3: Add the tens place: 4 + 2 + 1 (carry over) = 7. Write down 7 in the tens place. Step 4: Combine the digits: 73. So, 48 + 25 = 73. Liam now has 73 trading cards.

6. Noah is building a bookshelf for his classroom. He needs to cut a long board into equal pieces. The board is 96 inches long, and each shelf needs to be 8 inches long. How many shelves can Noah cut from the board? Answer: 12 Solution: Identify the total length of the board: 96 inches. Identify the length needed for each shelf: 8 inches.
   Full step-by-step solution

   Step 1: Identify the total length of the board: 96 inches. Step 2: Identify the length needed for each shelf: 8 inches. Step 3: To find out how many 8-inch shelves can be made from a 96-inch board, we divide the total length by the length per shelf: 96 ÷ 8. Step 4: Calculate the division: 96 ÷ 8 = 12. The answer is 12 shelves.

7. 699 + 125 = ? Answer: 824 Solution: Notice that 699 is very close to 700. Add 700 + 125 = 825. Since we added 1 extra (700 - 699 = 1), subtract 1 from the result.
   Full step-by-step solution

   Step 1: Notice that 699 is very close to 700. Step 2: Add 700 + 125 = 825. Step 3: Since we added 1 extra (700 - 699 = 1), subtract 1 from the result. Step 4: 825 - 1 = 824. The answer is 824.

8. 497 + 168 = ? Answer: 665 Solution: Notice that 497 is very close to 500. Add 500 + 168 = 668. Since we added 3 extra (500 - 497 = 3), subtract 3 from the result.
   Full step-by-step solution

   Step 1: Notice that 497 is very close to 500. Step 2: Add 500 + 168 = 668. Step 3: Since we added 3 extra (500 - 497 = 3), subtract 3 from the result. Step 4: 668 - 3 = 665. The answer is 665.