## iGreen one year ago Solved

1. iGreen

What are the expected number of flights on time?

2. acxbox22

use proportions

3. mathstudent55

Since 84% of the flights in the random sample are on time, we expect the same percentage to be on time in general. 84% means 84 out of 100.

4. iGreen

Whoa..major lag

5. mathstudent55

$$\dfrac{84}{100} = \dfrac{x}{203}$$

6. Astrophysics

7. iGreen

I came up with .84 * 203 or 170.52

8. Astrophysics

That sounds right

9. mathstudent55

You can think of the proportion as follows: 84 flights out of 100 are on time just like x flights out of 203 are on time.

10. Astrophysics

170.52

11. iGreen

I was trying to say that before anyone else commented..for some reason I can only make one comment and it glitches and I have to reload..

12. mathstudent55

Correct. I'd round it off to 171 because I don't know what 0.52 of a flight is.

13. iGreen

Okay, now it asks: "What is the standard deviation?"

14. iGreen

Any idea on how to find that? @mathstudent55

15. iGreen

16. Astrophysics

Standard deviation is the average difference between any point of data and the mean, been a long time since I did statistics but I'm sure we can figure it out. $\sigma = \sqrt{\frac{ 1 }{ N }\sum_{i=1}^{N}(x_i-\mu)^2}$

17. Astrophysics

But for this the easiest way I see is we can just use $\sigma = \sqrt{npq}$ where $\mu = \sqrt{np}$ that should be easy enough :P

18. iGreen

Ahhh

19. iGreen

I got 5.22

20. Astrophysics

That sounds good!

21. iGreen

$$\sf \sqrt{260 \times 0.84 \times 0.16}$$

22. iGreen

Thanks!

23. Astrophysics

Np