Personal Finance Big Ideas taught in this task:
- Popsicle sticks and rubber bands or base-10 blocks
- Paper and pencil for each student
The teacher should pose the following question to students:
Louis wants to give $15 to help kids who need school supplies. He also wants to buy a pair of shoes for $39. If Louis gets $1 every day for his allowance, how many days will it take him to save enough money for both? Explain how you know.
The purpose of this task is for students to relate addition and subtraction problems to money and to situations and goals related to saving money. This problem can be adjusted based on where students are in their understanding of addition involving two digit numbers. This task has students adding two 2-digit numbers that require regrouping, and is therefore the most advanced type of addition problem that first graders will encounter. As a result, this is a very challenging instructional task for first grade students and they should have access to the appropriate tools when working on it. 1.NBT.4 also indicates that students should be able to add a 1-digit number to a 2-digit number and a 2-digit number and a multiple of 10 with greater fluency than two two-digit numbers. If students are working on either of these simpler types of problems, then the item that Louis wants to buy for himself could be, for example, a trip to the movies for $8 or a toy for $20. The second solution shows how students who can mentally add 10 to a 2-digit number without counting (see 1.NBT.5) might approach the task.
Teachers can make the problem more personal by letting the student choose a toy he/she wants and the toy their sibling or friend may want and researching the costs. If students do this type of research, they will be engaging in MP 4, Model with mathematics. Students can also choose how much money they want to donate and for what cause. If the students in the class don’t receive allowance, the child in the task can make money by helping a neighbor (perhaps walking a dog or bringing in the mail).
To see a task with the same context that shows the mathematical work that second grade students will be doing around multi-digit addition, see 2.OA, NBT Saving Money 2 .
This task is part of a set collaboratively developed by Money as You Learn, an initiative inspired by recommendations of the President’s Advisory Council on Financial Capability, and Illustrative Mathematics. Integrating essential financial literacy concepts into the teaching of the Common Core State Standards can strengthen teaching of the Common Core and expose students to knowledge and skills they need to become financially capable young adults. A mapping of essential personal finance concepts and skills against the Common Core State Standards as well as additional tasks and texts will be available at www.moneyasyoulearn.org. This task and additional personal finance-related mathematics tasks are available at www.illustrativemathematics.org and are tagged “financial literacy.”
SOLUTION: USING BUNDLED OBJECTS
To find out how much money he needs to save, we will find 15 + 39. First, let’s represent 15 with 1 bundle of ten and 5 single sticks and 39 with 3 bundles of ten and 9 single sticks:
If we put the tens together and the ones together, we have 4 bundles of ten, and 5 singles and another 9 singles:
If we take 5 singles from the 9 and put them with the other 5:
we can make another bundle of ten:
(Students might also take 1 from the five and put it with the 9 to make 10.)
Now we have 5 bundles of ten and 4 singles, which represents 54. Since he gets $1 per day, it will take him 54 days to save for both.
SOLUTION: USING AN EMPTY NUMBER LINE
To find out how much money he needs to save, we will find 15 + 39.
We can start at 15, then count up by tens 3 times, then count up by ones 9 times:
It is actually more efficient to start with 39 and add 15 to it; some students will recognize this:
Since he gets $1 per day, it will take him 54 days to save for both.