Math Riddles for Adults

Instructor: Shelby Golden
Check out these fun riddles to practice various mathematical skills. This article includes solutions to the riddles and additional educational resources that can help you become proficient in various math topics.

Prime Numbers

You have three prime numbers, and they equal 100 when you add them together. You know nothing about your numbers except that one is less than a half but more than a third of one of the others. What are your numbers?

  • Solution: Because your numbers equal 100, one of them must be even. There is only one even prime (2). Your other numbers must, therefore, equal 98. Going through the other prime numbers, you will find that the other numbers must be 67 and 31.

Quick Tip:

Prime numbers are reviewed in this lesson on prime factorization. You can watch this short lesson to learn about the typical ways of finding a number's prime factors.

Geometric Shapes

You have a perfect cube. Can you divide your cube into smaller cubes that all have different volumes?

  • Solution: No. There is no way for cubes of all different volumes to correctly fit inside of a larger cube. There would be empty spaces as the cubes got smaller and smaller and you would have no way to fill these spaces. Eventually, the cubes would be too small to continue.

Quick Tip:

You can use this lesson on three-dimensional shapes to find out about the characteristics of these types of shapes. This lesson on finding the volume of a cube can also strengthen your understanding of the formula used to calculate the volume of this 3D shape.


One morning you need to find some socks, but your light is broken. You know there are 10 purple socks and 10 orange socks in your drawer, but they're all mixed up. They are completely the same except for their color. How many socks do you have to pick to ensure you have a matching pair?

  • Solution: You only have to pick 3 socks. Because there are only two colors of socks in the drawer, you will definitely have a matching pair if you take 3 out of the room.

Quick Tip:

Focus on increasing your understanding of this subject with this lesson on the probability of dependent and independent events. This video is a great way to quickly go over the rules that govern probability.

Word Problems

You are cutting up a pie. First you cut it into two pieces. With your next cut, you produce 4 pieces. The third cut results in 7 pieces. How many pieces can you cut with seven slices?

  • Solution: Solve this problem by considering the rule established by the slices. 1 cut makes 2 pieces. A second cut makes 4, and a 3rd makes 7. So each cut increases the number of pieces by the number of the cut (1, 2 and 3). Therefore, the 4th cut will add 4 pieces, the 5th cut will add 5, the 6th will add 6 and the 7th will add 7. Added together, this equals 29 pieces of pie.

Quick Tip:

You can brush up on your ability to solve word problems with these lessons on the steps for solving word problems and how to solve word problems with multiple steps. Evaluate your comprehension of the material presented in these resources by taking a self-assessment quiz at the end of each lesson.

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