Complete the Addition Sentence (Algebra!)
𧩠The Missing Piece! You know the start, you know the total. Now use backwards math to find what's missing in the middle!
Do this: Read the concept below, then try the quiz or activity.
Concept
This is Algebra! But instead of the letter "X", it's just a blank space.
π― The "Opposite math" Rule: Problem: 325 + _____ = 850
If you have to add two numbers to get a total, then the difference between the Total and the Start is perfectly equal to the missing piece!
1. Take the Total (the biggest number): 850. 2. SUBTRACT the piece you already know: 325. 3. Do the math! (850 - 325). 8 5 0 - 3 2 5 --------- (Borrow from the 5, make 10. 10 - 5 = 5. Tens: 4-2=2. Hundreds: 8-3=5.) 4. Answer: 525!
Let's check it! 325 + 525 = 850. It works perfectly.
Try it
Find the missing puzzle piece!
Instructions: Take the Total, subtracting the piece you know!
Problem 1: 400 + _____ = 900 * Total: 900. Piece: 400. * Wait! Do you even need to stack this? Just use the dial! 9 - 4! * Answer: _____
Problem 2: 152 + _____ = 684 * 684 - 152 = ? * Answer: _____
Problem 3: _____ + 250 = 500 * Total: 500. Piece: 250. * Answer: _____
Problem 4: 399 + _____ = 500 * (Hint: Just count up! What is 399 plus 1?) * Answer: _____