The reason 2 X 5 X 9 is not the prime factorization of 90 is that 9 is not a Prime number. 3 X 3 is 9, so the prime factorization of 90 is 2 X 3 X 3 X 5.
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2 x 3 x 3 x 5 = 90
Prime Factorization of 90To find the prime factorization of 90, start with the lowest prime number that will divide into 90. That number is 2. 2 times 45 equals 90. 2 is a number in the prime factorization of 90. Next, find the lowest prime number that will divide into 45. The number is 3, and 3 times15 equals 45. 3 is one of the prime factors, so now you have 2 times 3 times 15. 15 is not a prime number, and the lowest prime number that will divide into 15. 3 times 5 is 15. You'll notice that both 3 and 5 are prime numbers, so the prime factorization of 90 is 2 X 3 X 3 X 5. Check your answer to make sure it is correct and you're done.
Ronald is correct, as 2x3x3x5 = 6x3x5 = 18x5 = 90. Ronald would have also been correct to put 2x32x5. Donald is incorrect, as 32x5 = 3x3x5 = 9x5 = 45.
30 and 90 are two of many numbers whose prime factors include 2, 3, and 5.