Finding What Went Away
Finding what went away in a subtraction word problem means calculating the amount that was removed or sent from a starting quantity, using the formula: starting amount minus leftover amount equals amount that went away. In 4th grade math with Saxon Math Intermediate 4, Chapter 3, students practice this by subtracting the ending value from the starting value — for example, if you started with 42 shells and ended with 29, then 42 - 29 = 13 shells went away. This teaches students to recognize the subtraction structure in separation stories.
Key Concepts
Property To find the amount that 'went away', solve for the middle number: $a s = l$.
Examples Celia had 42 shells and ended with 29. She sent away $42 29 = 13$ shells. Marko had 42 cards and now has 26. He mailed $42 26 = 16$ cards.
Explanation To figure out how many items vanished, subtract what's left from your starting amount. The difference is the missing 'went away' number. It's a simple subtraction puzzle!
Common Questions
How do you find what went away in a subtraction problem?
Subtract the amount you have left (the ending amount) from the amount you started with (the starting amount). The difference is what went away. Formula: starting amount - leftover = amount that went away.
What is an example of finding what went away?
Celia started with 42 shells and now has 29. How many went away? 42 - 29 = 13. So 13 shells went away.
What type of word problem involves finding what went away?
These are called separation or take-away problems. They describe a situation where a starting amount is reduced by some quantity being removed, sent, or used, and you need to find how much was removed.
How is finding what went away different from finding the starting amount?
Finding what went away means you know the start and end and calculate the middle (what was removed). Finding the starting amount means you know the removed part and the end, and you add them to get the original total.
When do 4th graders practice finding what went away?
In Saxon Math Intermediate 4, Chapter 3, Lessons 21-30, students practice the three subtraction story structures: finding the ending amount, finding the starting amount, and finding what went away.
Why is it important to identify the problem structure in subtraction word problems?
Knowing which quantity is unknown (the end, the start, or the middle) tells you exactly what calculation to perform. This prevents students from defaulting to the wrong operation just because a problem uses subtraction vocabulary.