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Find the Number – become familiar with the rules for divisibility

Now that students have become familiar with the rules for divisibility, offer them another challenge.

Divide the class up into groups and give them this problem:

In the next 15 minutes they must write down as many numbers as possible that they think can be divided by the numbers 2, 3, and 5. The numbers they write can be divisible by other numbers as well, of course, but every number they write must be divisible by all three numbers.

They can work together to come up with their numbers or they can write their numbers down and then compare their individual answers to come up with their final answers.

When the 15 minutes are over, check all the student answers. The group that comes up with the most correct numbers and NO incorrect numbers is the winner of this challenge! If they write an incorrect number, they are disqualified.

You can check right away and eliminate all numbers that don’t end in 0 since the numbers they write must be divisible by 2 x 5 or 10.

In the next 15 minutes you must write down as many numbers as possible that you think can be divided by the numbers 2, 3, and 5.

The numbers you write can be divisible by other numbers as well, of course, but every number you write must be divisible by ALL three numbers.

Now that your students have had some practice coming up with numbers that are divisible by 2, 3, and 5 it’s time to ask them some questions on HOW they came up with those numbers.

Here are some questions to stimulate their thinking:

1)How do you know that the number 253 is NOT divisible by 2, 3, and 5? (even though the numbers 2, 3, and 5 are visible in the number 253, it can’t be divided evenly by any combination of the numbers 2, 3 or 5…it doesn’t fit any of these divisibility rules)

1)What is the smallest number that is divisible by 2, 3, and 5? (students will soon figure out that 2 x 3 x 5 will give them that answer)

2)Does a number divisible by 2, 3, and 5 always end in 0? (Yes, because it must be divisible by 2 x 5 or 10)

3)Can you come up with a simple way to show a pattern of numbers that are divisible by 2, 3, and 5? (one way is to put a zero at the end and make sure that the digits added together are divisible by 3)

 

For example, 30, 60, 90, 120, 150, 720, 810, 900, 1230, etc. are all divisible by all three numbers.

 

Focus on Division

Doing division should be fun because if you can inspire a child's mind to enjoy division, they will do much better at it, and that will lead to future success. In total, Focus on Division has 19 division games, 28 division activities, a huge collection of fun divisibility mazes (worksheets) & 17 Multiply & Divide Poster/Anchor Charts with Cards for Students that will make division more enjoyable.

Focus on Division has a rich selection of interesting and fun math games to choose from. It makes for a great center unit when learning the basics of division and multiplication, and the kids will have a blast, which means that they will be more receptive to the teaching.

Download the Focus on Division Bundle Here!

 

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