I am taking Applied Stats in college. I haven't taken a math class for several years and was never any good with it to begin with. I am just not comprehending any of this. It is my first two weeks so we are working on:
Standard deviations
Variance of a random variable
Discrete probability for a random variable
Standard deviation of random variable
If someone can explain these things in the simplest of ways, if that's possible, I'd greatly appreciate it.
I will feel like I am starting to understand a formula and then my answers are wrong and I can't figure out what I have done. My professor is not very helpful, plus I am taking online classes so I am not really getting any hands-on assistance here…
Example problem that I am stuck on:
Construct a discrete random probability distribution for the random variable X
P(x,) = f,/N
N = (f,+f,…)
N = 4
X f
4 P(4) = 15/80 = 0.1875
5 P(5) = 11/80 = 0.1375
6 P(6) = 16/80 = 0.2
7 P(7) = 38/80 = 0.475
(The above answers were put in and came out being correct)
The second part...
Mean of the random variable X
Mean = Sum of [x * P(x)]
4(0.1875) + 5(0.1375) + 6(0.2) + 7(0.475)
= 0.75 + 0.6875 + 1.2 + 3.325
=5.9625
Now I am supposed to find the standard deviation of the variable x, which is apparently a different thing altogether and I am stuck. It gave me the formula:
Square Root Of {Standard Dev. of Variable X = Sum of [X2 * P(x)] - Mean of the random variable X (or the "sum of [x*P(x)] problem)}
When I tried this I got...
[42(0.1875) + 52(0.1375) + 62(0.2) + 72(0.475)] - 5.9625
= 3 + 3.4375 + 7.2 + 23.275
= 36.9125 - 5.9625
= 30.95
Square root: 5.5633
That was not right as the answer was supposed to be 1.2 (after rounding) and I just don't understand what I did wrong here….
Again, I am not really comprehending these as it seems the formulas change every time there is another question. I might just have trouble interpreting the question/answer but I am not sure.
--Bianca
Standard deviations
Variance of a random variable
Discrete probability for a random variable
Standard deviation of random variable
If someone can explain these things in the simplest of ways, if that's possible, I'd greatly appreciate it.
I will feel like I am starting to understand a formula and then my answers are wrong and I can't figure out what I have done. My professor is not very helpful, plus I am taking online classes so I am not really getting any hands-on assistance here…
Example problem that I am stuck on:
Construct a discrete random probability distribution for the random variable X
P(x,) = f,/N
N = (f,+f,…)
N = 4
X f
4 P(4) = 15/80 = 0.1875
5 P(5) = 11/80 = 0.1375
6 P(6) = 16/80 = 0.2
7 P(7) = 38/80 = 0.475
(The above answers were put in and came out being correct)
The second part...
Mean of the random variable X
Mean = Sum of [x * P(x)]
4(0.1875) + 5(0.1375) + 6(0.2) + 7(0.475)
= 0.75 + 0.6875 + 1.2 + 3.325
=5.9625
Now I am supposed to find the standard deviation of the variable x, which is apparently a different thing altogether and I am stuck. It gave me the formula:
Square Root Of {Standard Dev. of Variable X = Sum of [X2 * P(x)] - Mean of the random variable X (or the "sum of [x*P(x)] problem)}
When I tried this I got...
[42(0.1875) + 52(0.1375) + 62(0.2) + 72(0.475)] - 5.9625
= 3 + 3.4375 + 7.2 + 23.275
= 36.9125 - 5.9625
= 30.95
Square root: 5.5633
That was not right as the answer was supposed to be 1.2 (after rounding) and I just don't understand what I did wrong here….
Again, I am not really comprehending these as it seems the formulas change every time there is another question. I might just have trouble interpreting the question/answer but I am not sure.
--Bianca