Add/Subtract Decimals

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Answer Key & Explanations

Add/Subtract Decimals · Grade 4 · Worksheet 3

1. A rectangular playground is drawn on a map with a length of 25.75 meters and a width of 18.5 meters. A running track is planned to go around the entire outside edge of the playground. What is the total length of the running track in meters? Answer: 88.5 Solution: Recall the formula for the perimeter of a rectangle. Perimeter = 2 × (length + width) Substitute the given values into the formula. Perimeter = 2 × (25.75 + 18.5) Add the length and width.
   Full step-by-step solution

   Step 1: Recall the formula for the perimeter of a rectangle. Perimeter = 2 × (length + width) Step 2: Substitute the given values into the formula. Perimeter = 2 × (25.75 + 18.5) Step 3: Add the length and width. 25.75 + 18.5 = 44.25 Step 4: Multiply the sum by 2. 2 × 44.25 = 88.5 Step 5: State the final answer. The total length of the running track is 88.5 meters.

2. Nikau had 38 dollars. Then Nikau spent 2 dollars at the store. How much money does Nikau have left? Answer: 36 Solution: Start with 38 dollars. Subtract the amount spent: 38 - 2 = 36. Nikau has 36 dollars left.
   Full step-by-step solution

   Step 1: Start with 38 dollars. Step 2: Subtract the amount spent: 38 - 2 = 36. Nikau has 36 dollars left.

3. Sophia is training for a marathon. On Saturday, she ran 12.75 kilometers. On Sunday, she ran 15.25 kilometers. How many total kilometers did Sophia run over the weekend? Answer: 28.00 Solution: Identify the distances Sophia ran each day. Saturday: 12.75 km Sunday: 15.25 km Write the numbers vertically, aligning the decimal points. 12.75 + 15.25 Add the hundredths place.
   Full step-by-step solution

   Step 1: Identify the distances Sophia ran each day. Saturday: 12.75 km Sunday: 15.25 km Step 2: Write the numbers vertically, aligning the decimal points. 12.75 + 15.25 ________ Step 3: Add the hundredths place. 5 hundredths + 5 hundredths = 10 hundredths 10 hundredths = 1 tenth and 0 hundredths Write 0 in the hundredths place and carry 1 to the tenths place. Step 4: Add the tenths place. 7 tenths + 2 tenths = 9 tenths Plus the carried 1 tenth = 10 tenths 10 tenths = 1 whole and 0 tenths Write 0 in the tenths place and carry 1 to the ones place. Step 5: Add the ones place. 2 ones + 5 ones = 7 ones Plus the carried 1 one = 8 ones Write 8 in the ones place. Step 6: Add the tens place. 1 ten + 1 ten = 2 tens Write 2 in the tens place. Step 7: Combine all the results. The total is 28.00 Sophia ran 28.00 kilometers total over the weekend.

4. Maria is measuring ribbon for a craft project. She has a piece that is 2.45 meters long. She cuts off 0.85 meters to use for one part of her project. How many meters of ribbon does she have left? Write your answer as a decimal. Answer: 1.60 Solution: Maria starts with a ribbon that is 2.45 meters long. She cuts off 0.85 meters. To find out how much ribbon is left, we subtract the length she cut from the original length.
   Full step-by-step solution

   Maria starts with a ribbon that is 2.45 meters long. She cuts off 0.85 meters. To find out how much ribbon is left, we subtract the length she cut from the original length. Step 1: Write the subtraction problem. 2.45 - 0.85 Step 2: Align the decimal points and subtract digit by digit from right to left. 2.45 - 0.85 Step 3: Start from the hundredths place (rightmost digits). 5 hundredths - 5 hundredths = 0 hundredths. Write 0 in the hundredths place. Step 4: Move to the tenths place. 4 tenths - 8 tenths cannot be done directly, so we borrow 1 from the units place. The 2 in the units place becomes 1, and the 4 tenths become 14 tenths. Step 5: Now subtract in the tenths place: 14 tenths - 8 tenths = 6 tenths. Write 6 in the tenths place. Step 6: Subtract in the units place: 1 unit - 0 units = 1 unit. Write 1 in the units place. Step 7: The result is 1.60 meters. So, Maria has 1.60 meters of ribbon left.

5. Maria is training for a 5K race. On Monday she ran 3.25 kilometers and on Wednesday she ran 2.75 kilometers. How many total kilometers did Maria run during these two training sessions? Answer: 6.00 Solution: Monday: 3.25 kilometers Wednesday: 2.75 kilometers 3 + 2 = 5 0.25 + 0.75 = 1.00 5 + 1.00 = 6.00 Maria ran 6.00 kilometers total during these two training sessions.
   Full step-by-step solution

   Step 1: Write down the distances Maria ran each day Monday: 3.25 kilometers Wednesday: 2.75 kilometers Step 2: Add the whole number parts 3 + 2 = 5 Step 3: Add the decimal parts 0.25 + 0.75 = 1.00 Step 4: Combine the results 5 + 1.00 = 6.00 Maria ran 6.00 kilometers total during these two training sessions.

6. 23.45 + 17.89 = ? Answer: 41.34 Solution: Write the numbers vertically, aligning the decimal points. 23.45 + 17.89 Add the numbers in the hundredths place: 5 + 9 = 14. Write down 4 in the hundredths place and carry over 1 to the tenths place.
   Full step-by-step solution

   Step 1: Write the numbers vertically, aligning the decimal points. 23.45 + 17.89 -------- Step 2: Add the numbers in the hundredths place: 5 + 9 = 14. Write down 4 in the hundredths place and carry over 1 to the tenths place. Step 3: Add the numbers in the tenths place: 4 + 8 + 1 (carried over) = 13. Write down 3 in the tenths place and carry over 1 to the ones place. Step 4: Add the numbers in the ones place: 3 + 7 + 1 (carried over) = 11. Write down 1 in the ones place and carry over 1 to the tens place. Step 5: Add the numbers in the tens place: 2 + 1 + 1 (carried over) = 4. Write down 4 in the tens place. Step 6: Bring down the decimal point. The final answer is 41.34.

7. 12.75 + 8.25 = ? Answer: 21.00 Solution: Write the numbers one above the other, aligning the decimal points. 12.75 + 8.25 Start adding from the rightmost column (hundredths place). The hundredths column: 5 (from 12.75) + 5 (from 8.25) = 10.
   Full step-by-step solution

   Let's add 12.75 and 8.25 step-by-step. Step 1: Write the numbers one above the other, aligning the decimal points. 12.75 + 8.25 --------- Step 2: Start adding from the rightmost column (hundredths place). The hundredths column: 5 (from 12.75) + 5 (from 8.25) = 10. Write down 0 in the hundredths place, and carry over 1 to the tenths place. Step 3: Add the tenths place, including the carry-over. Tenths column: 7 (from 12.75) + 2 (from 8.25) + 1 (carried over) = 10. Write down 0 in the tenths place, and carry over 1 to the units (ones) place. Step 4: Add the units (ones) place, including the carry-over. Units column: 2 (from 12.75) + 8 (from 8.25) + 1 (carried over) = 11. Write down 1 in the units place, and carry over 1 to the tens place. Step 5: Add the tens place, including the carry-over. Tens column: 1 (from 12.75) + 0 (from 8.25, since there is no digit) + 1 (carried over) = 2. Write down 2 in the tens place. Step 6: Combine all digits, placing the decimal point in the same aligned position. We have: 2 (tens), 1 (units), decimal point, 0 (tenths), 0 (hundredths) → 21.00 Final Answer: 21.00