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write 225 as a product of prime factors

The last digit is a 5, so 225 is divisible by 5. 2+2+5 is 9, divisible by 3, so 225 is divisible by 3. That's two numbers to get you going.
13 January 2012
To write any number as a product of prime factors, you look at the number and try to see what prime numbers you can divide it by. It's clearly divisible by 5, so you divide it by 5. 225/5=45. Then you look at that number, and repeat the process, in this case dividing by 5 again. 45/5=9 So you look at 9, and see that it's divisible by 3. 9/3=3 Then you know you have finished, because you have come to a number that will not divide further, because it is itself a prime number. Therefore, the prime factors of 225 are the numbers you divided it by until you made it prime, including the last prime you arrived at. Prime factors are: 5, 5, 3, 3.
17 January 2012
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