Each of 8 samples has a different standard deviation. How many of the 8 samples could be from the same population?
2 answers:
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1. 
is a 2nd degree polynomial, so if it can be factorize, it can be factorized into two 1st degree polynomials:
2. consider the factorized expression. If we factorized back we would get:
3. So
comparing the coefficients, we see that
a+b=4 and ab=-5.
From ab=-5, a is either 5 (b=-1) or a is -5 (b=1). Together with the condition a+b=4, we see that the right choice is a=5 and b=-1
4. so
5. The factors are x-5 and x+1
2. consider the factorized expression. If we factorized back we would get:
3. So
comparing the coefficients, we see that
a+b=4 and ab=-5.
From ab=-5, a is either 5 (b=-1) or a is -5 (b=1). Together with the condition a+b=4, we see that the right choice is a=5 and b=-1
4. so
5. The factors are x-5 and x+1