Is 183,243,042 divisible by 3?
You might think the only thing you can do is find the nearest calculator or perhaps hunker down for a wildly tedious bout of long division, however, there's an easier way to tell for 3 (and others!)
A NUMBER IS DIVISIBLE BY 1:
A NUMBER IS DIVISIBLE BY 2:
If it is even. This is actually what it means to be even, but just check that last digit for a 2,4,6,8, or 0.
(Example: 48,183,380 is divisible by 2 because the last digit is 0)
A NUMBER IS DIVISIBLE BY 3:
If the sum of the digits is divisible by 3.
Consider the above example (183,243,042). Well it is! 1+8+3+2+4+3+0+4+2 = 27 and 27 is divisible by 3.
A NUMBER IS DIVISIBLE BY 4:
If the last two digits form a number divisible by 4.
(Example: 32,416 is divisible by 4 because 16 is!)
A NUMBER IS DIVISIBLE BY 5:
If the last digit is either a 0 or a 5
(Example: Both 285 and 6,420 are divisible by 5)
A NUMBER IS DIVISIBLE BY 6:
If the number is divisible by both 2 and 3 (By the above rules)
(Example: Our original number 183,243,042 is divisible by 6!)
A NUMBER IS DIVISIBLE BY 7: (TRICKY!)
Double the last digit and subtract it from the remaining digits, is that divisible by 7?
(Example: 371 is divisible by 7 because 37-2 = 35, and 35 is divisible by 7)
A NUMBER IS DIVISIBLE BY 8:
When the last 3 digits form a number divisible by 8
(Example: 300,000,000,104 is divisible by 8 because 104 is.)
A NUMBER IS DIVISIBLE BY 9:
If the sum of the digits is divisible by 9 (just like the rule for 3!)
(Example: 45 is divisible by 9 because 4+5=9, and 9 is divisible by 9)
A NUMBER IS DIVISIBLE BY 10:
If the last digit is 0
(Example: 30, 270, 610 are all divisible by 10.)