Beacon Lesson Plan Library

And the Number Is (Second Grade)

Kathy Peters
Bay District Schools


Students create their own Mystery Numbers by giving clues about the name, value, and multiples of the digits which comprise the number.


The student names whole numbers combining 3-digit numeration (hundreds, tens, ones) and the use of number periods, such as ones, thousands, and millions and associates verbal names, written word names, and standard numerals with whole numbers, commonly used fractions, decimals, and percents.

The student uses place-value concepts of grouping based upon powers of ten (thousandths, hundredths, tenths, ones, tens, hundreds, thousands) within the decimal number system.

The student understands and applies basic number theory concepts, including primes, composites, factors, and multiples.


-Computer with Internet access to online student lesson, -Guess My Number- (optional for reinforcement; see Weblinks)
-Index Cards
-Chart listing problem-solving skills (see Preparation)
-Mystery Numbers overhead transparency (download from Associated File)
-Mystery Number Checklist (one per student, download from Associated File)
-Overhead projector and pens


1. Make sure computers are online and the lesson, -Guess My Number,- is bookmarked (see Resources for address). Preview lesson for content.
2. Prepare and post a chart that lists problem-solving skills (see part II of Procedures).
3. Have index cards handy for students to write Mystery Number clues on.
4. Download Mystery Numbers master from Associated Files and make an overhead transparency.
5. Download Mystery Number Checklist and make one copy per student.


I. Introduce Lesson: Today we are going to play a game with numbers I call -And the number is...- I will give you clues about the number, and you are going to problem solve to determine what that number is. This is a way to play with numbers and learn more about how numbers work.

II. First, let us review the problem- solving skills we need to use. Refer to a chart that displays the following:
1. Read or listen to all information first.
2. Write down important information.
3. Think!
4. Check your answer by going over the clues.

Review all other important mathematical concepts needed to play this game (Your students should already be familiar with these concepts.)
1. What is a digit?
2. What do digits have to do with place value?
3. What do I mean by odd and even numbers?
4. What do I mean by the word multiple? addend?
5. What do I mean by the words sum and product?
Discuss as appropriate to your students.

III. Now, let's get started. All you need is paper and pencil. Remember to use your problem solving skills and those number concepts we have just talked about. Display -Mystery Numbers- master (see Resources) on the overhead and discuss each orally as a whole group as follows:

Mystery Number One
Here are your clues!
I call this a Level 1.
First clue - I am a two-digit number.
Second clue - My tens digit is a multiple of my ones digit.
Third clue - The sum of my digits is nine.
And the number is?_____

After posing this set of clues, allow students time to discuss possibilities with a partner. While they are doing this, represent the number visually with a model, in expanded notation, or in words so students can check their answers. Students then check their answers with your representation and against the number that answers the clues.

Follow the same procedure for each of the remaining Mystery Numbers.

Mystery Number Two
Here are your clues!
I call this a Level 2.
First clue - I am a three-digit number.
Second clue - I am an odd number.
Third clue - All my digits are the same.
Fourth clue - The product of my digits is 27.
And the number is?______

Mystery Number Three
Here are your clues!
I call this a Level 3.
First clue - I am a four-digit number.
Second clue - My ones digit is a four.
Third clue - My thousands digit is twice the value of the ones digit.
Fourth clue - My hundreds digit is one less than the thousands digit.
Fifth clue - The sum of my digits is 25.
And the number is?______

Mystery Number Four
Let's do another Level 3.
First clue - I am a ___digit number.
Right! You're catching on. A Level 3 problem involves a four-digit number.
Second clue - My thousands digit is even and is a multiple of three.
Third clue - My ones digit is an even number and one less than my tens digit.
Fourth clue - My hundreds digit is three more than my thousands digit.
Fifth clue - My tens digit is equal to my hundreds digit.
And the number is?_______

KEY: MYSTERY NUMBER 1 = 63; 2 = 333; 3 = 8764; 4 = 6998

IV. Now, students write three mystery numbers of their own on index cards using the Mystery Number Checklist (see Resources).
1. Write clues for each level and be sure to solve your own mystery.
2. You need to use correct mathematical vocabulary.
3. You need to include odd and even numbers and operations such as addition and multiplication.
4. Use the Mystery Number Checklist to guide you through the process.
5. Draw a model, write the number in expanded notation, or write the number in words on the back of your card so other students can check their problem-solving skills.

V. When students finish creating their Mystery Numbers, they share with other students by posting them on a bulletin board. Students continue to practice their problem-solving skills by solving for Mystery Numbers. Students can also visit the computer and complete the online student lesson entitled, -Guess My Numbers-.


Lesson assessment is woven into the learning activity through the creation of the three mystery number clue cards. The Mystery Number Checklist (see Resources) is the assessment tool used by students to check their performance. It details the criteria and students can score a maximum of 120 points (8 points per item).


Students need prerequisite knowledge of writing numbers in expanded notation and in words and representing numbers with models. As students work through the online student lesson, -Guess My Number,- a broader variety of number clues are given incorporating basic number theory concepts. The Mystery Number clues could be expanded to include numbers of greater value.

Web Links

Web supplement for And the Number Is... This is an interactive Student Web Lesson.
Guess My Number

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