Finding Differences by Counting Up or Down
Finding Differences by Counting Up or Down is a Grade 4 math skill in enVision Mathematics, Chapter 2: Fluently Add and Subtract Multi-Digit Whole Numbers. Students learn two mental math strategies: counting up from the smaller number to the larger, or counting down from the larger in manageable parts.
Key Concepts
Property To find the difference between two numbers, you can either count up from the smaller number to the larger number, or count down from the larger number in parts. For $a b = c$, you can find $c$ by adding up from $b$ to $a$, or by subtracting parts of $b$ from $a$.
Examples Counting Up to find $4825 4578$: Start at 4578. Add 22 to get 4600. Then add 200 to get 4800. Finally, add 25 to get 4825. The difference is the sum of what you added: $22 + 200 + 25 = 247$.
Counting Down to find $9034 5276$: Start at 9034. Break apart 5276 into 5000 and 276. First, subtract 5000 from 9034: $9034 5000 = 4034$. Then, subtract 276 from 4034: $4034 276 = 3758$. So, $9034 5276 = 3758$.
Common Questions
What is the count up strategy for subtraction?
Start at the smaller number and add friendly amounts to reach the larger number. The sum of all the amounts you added is the difference.
What is the count down strategy for subtraction?
Start at the larger number and subtract the smaller number in manageable pieces, such as thousands then hundreds, until you reach the final answer.
How do you use count up to find 4825 minus 4578?
Start at 4578. Add 22 to reach 4600. Add 200 to reach 4800. Add 25 to reach 4825. The difference is 22 plus 200 plus 25 equals 247.
When should you use counting up vs counting down for subtraction?
Count up when the numbers are close together. Count down when the subtracted number is easy to break into place value parts. Both are effective mental math strategies.
What chapter covers counting up and down for subtraction in enVision Grade 4?
Finding differences by counting up or down is covered in Chapter 2: Fluently Add and Subtract Multi-Digit Whole Numbers in enVision Mathematics Grade 4.