Math Circles Prime Time Worksheet With Answers - Grade 6 - University Of Waterloo - 2015 Page 7
ADVERTISEMENT
1
2
3
4
5
6
7
8
9
10Divisibility
When you’re checking if a number is prime, you normally check to see if it’s divisible by
smaller numbers. You could answer questions about divisibility using long division, but
mathematicians are lazy and long division would take too much time. Instead, we have
discovered some neat tricks to speed up the process. Some of the simplest and most common
can be found in the table below.
Divisible by: Test:
2
The last digit in the number is even
3
The sum of all the digits is divisible by 3
4
The last two digits are divisible by 4
5
The number ends in 0 or 5
6
The number is divisible by 2 and 3
8
The last three digits are divisible by 8
Note: Can’t use this rule for numbers less than 1000
9
The sum of the digits is divisible by 9
10
The number ends in 0
11
The alternating sum of the digits is divisible by 11
Notes: Start with subtraction. 0 is divisible by 11
12
The number is divisible by 3 and 4
Try it out:
1. Is 34 627 888 divisible by 8?
Yes, since the last three digits (888) are divisible by 8.
2. Is 457 925 divisible by 9?
No, since the sum of the digits (32) is not divisible by 9.
3. Is 6756 divisible by 12?
Yes, since it is divisible by 3 and 4.
7
ADVERTISEMENT
0 votes
Related Articles
Related forms
Related Categories
Parent category: Education