Math Is Fun Forum

what if you need to know if you can reduce a large fraction down? Well one way to know if a fraction is divisible by 3 is to add up individual digits of the whole. If they add up a number that is divisible by 3 the large number is also divisible by 3. example. 1242 is divisible by 3 because 1+2+4+2=9 and 3 into 9 goes 3 times. chances are the number will also be divisible by 6 or 9 and sometimes both if it is divisible by 3. example 99 (9+9=18) is divisible by 3. 3 into 18 goes 6 times. But 99 is also divisible by 9. 9 x 11= 99.