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roastedchips
If x is a prime number, what is the number of different factors of 18x?
1) x^2 has 3 factors
2) x>3

the answer would depend on if x is a factor of 18, that is if x is 2 or 3
If x is 2 or 3, Ans will be different ..
    a) x=2, 18*2=\(2^2*3^2....(2+1)(2+1)=3*3=9\)
    b) X=3, 18*3=2*3^3.......(1+2)(3+1)=3*4=12
If x is any other prime number, Ans will be different.
    \(18x=2*3^2*X.......(1+1)(2+1)(1+1)=2*3*2=12\)

1) \(x^2\) has 3 factors.
Just tells us that \(x^2 is square of a prime number\)
This is already known
Insufficient

2) X>3
now X is a prime number >3
Irrespective of the value of X, factors of 18x will be
18x=2*3^2*X
So factors are (1+1)(2+1)(1+1)=2*3*2=12
Sufficient

B
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Hi,
In these equations
Case 1: If x=2, then 18x = 2^2 * 3^2 , total number of factors = 3*3 = 9
Case 2: If x=3, then 18x = 2 * 3^3 , total number of factors = 2*4 = 8

How are you saying that total factor will be 9 or 8. What is this formula... I have never seen that.
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shaishav.281281
Hi,
In these equations
Case 1: If x=2, then 18x = 2^2 * 3^2 , total number of factors = 3*3 = 9
Case 2: If x=3, then 18x = 2 * 3^3 , total number of factors = 2*4 = 8

How are you saying that total factor will be 9 or 8. What is this formula... I have never seen that.


For finding number of positive factors, get the number in prime factorisation.
For example 72 = 2^3*3^2
Then, add one to each exponent and find their product => (3+1)(2+1) =12
Say number is \(x=a^p*b^q*c^r\), then number of factors are \((p+1)(q+1)(r+1)\)
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shaishav.281281
Hi,
In these equations
Case 1: If x=2, then 18x = 2^2 * 3^2 , total number of factors = 3*3 = 9
Case 2: If x=3, then 18x = 2 * 3^3 , total number of factors = 2*4 = 8

How are you saying that total factor will be 9 or 8. What is this formula... I have never seen that.

Let's see if I can help.

There is a rule I learned on TTP to evaluate the total number of factors (a.k.a. number of divisors) of a number.
Let me give an example to demonstrate how the rule works. Suppose we have to find the number of factors of the number 2160. If we decompose this number into primes, we will have: 2^4 x 3^3 x 5^1. To find out the number of factors, we have to multiply the powers plus 1. In this case, the total number of factors will be (4+1)x(3+1)x(1+1) = 40 factors.

I hope that helps to comprehend the rule
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