Word Problems: Result Unknown - First Grade Mathematics

Story problems come in different shapes and flavors, depending on which part of the story is a mystery! The most common and familiar type of word problem is called a Result Unknown problem. In a Result Unknown problem, the story tells you the starting amount and describes what changes, but the end result is a secret waiting to be found. In this chapter, you will learn how to identify Result Unknown stories in both addition and subtraction, draw clear models to represent the action, and solve for the unknown result.

Anatomy of a Result Unknown Problem

Every Result Unknown problem follows a simple timeline: Beginning -> Change -> What is the End?

The Result Unknown Timeline:
[ START AMOUNT ]  --->  [ THE CHANGE HAPPENS ]  --->  [ RESULT = ? ]
   (Known!)                    (Known!)                 (The Mystery!)

Two Types of Result Unknown Problems:

Type 1 (Add To - Result Unknown): You start with an amount, more items join, and you find the total result. Type 2 (Take From - Result Unknown): You start with an amount, some items leave, and you find the remaining result.

Example 1: Add To (Result Unknown)

Let us examine an addition story where the result is unknown.

The Story:
Elijah had 8 shiny marbles in his pocket.
On the playground, his friend gave him 5 more marbles.
How many marbles does Elijah have now?

Timeline Model:
Start:   8 marbles
Change:  + 5 marbles
Result:  ? marbles

Equation: 8 + 5 = ?
Solve: 8 + 2 = 10, plus 3 = 13.
Answer: Elijah has 13 marbles now!

Notice the Question:

The question asks: "How many does he have NOW?" This is the classic signature of a Result Unknown problem. You are calculating the final result after the change has taken place.

Example 2: Take From (Result Unknown)

Now let us look at a subtraction story where the result is unknown.

The Story:
There were 16 birds sitting on a telephone wire.
7 of the birds flew away to look for food.
How many birds were left on the telephone wire?

Timeline Model:
Start:   16 birds
Change:  - 7 birds
Result:  ? birds

Equation: 16 - 7 = ?
Solve (Think Addition): 7 + 9 = 16.
Answer: 9 birds were left on the telephone wire!

The Key Feature

In both examples, you know everything that happened at the beginning and middle of the story. You only have to calculate the ending!

Practice Exercises

Exercise 1: Read and solve: "Amelia has 9 books on her shelf. She visits the library and brings home 4 more books. How many books does Amelia have on her shelf now?" Write the equation and answer.

Exercise 2: Read and solve: "There were 15 strawberries in a bowl. Daniel ate 6 of them as an afternoon snack. How many strawberries are left in the bowl?" Write the equation and answer.

Exercise 3: Explain in your own words what makes a problem a "Result Unknown" problem.

Exercise 4: Write your own Result Unknown addition story problem using the numbers 7 and 6.

Solutions and Explanations

Solution to Exercise 1: Start = 9, Change = +4. Equation: 9 + 4 = 13. Amelia has 13 books on her shelf now.

Solution to Exercise 2: Start = 15, Change = -6. Equation: 15 - 6 = 9. There are 9 strawberries left in the bowl.

Solution to Exercise 3: A problem is "Result Unknown" when you are told the starting quantity and the exact amount that joined or left, and you only need to calculate the final outcome or total at the end of the story.

Solution to Exercise 4: Example story: "Lucas had 7 toy dinosaurs. For his birthday, his aunt gave him 6 more toy dinosaurs. How many toy dinosaurs does Lucas have in all now?" (Equation: 7 + 6 = 13).