Approximate the Prob. in a normal distribution of a binomial

[rogo0034]

Homework Statement

Homework Equations

The Attempt at a Solution

 

[rogo0034]

See, i was having trouble determining when to use the Continuity Correction in the problems, and i guess i still am. but i was able to match my answer with the given one from the back of the book when I stopped using it. however, the second problem doesn't match, even after using the new formula and the new percentage.

I got .3264 and they got .3974

Where am i going wrong here? anyone?

 

[Ray Vickson]

See, i was having trouble determining when to use the Continuity Correction in the problems, and i guess i still am. but i was able to match my answer with the given one from the back of the book when I stopped using it. however, the second problem doesn't match, even after using the new formula and the new percentage.

I got .3264 and they got .3974

Where am i going wrong here? anyone?

You should NOT use the continuity correction in (a), because you are NOT approximating a discrete distribution by a continuous one; you are evaluating a probability for a truly continuous random variable. So, you get a slightly wrong probability in (a), then you use that incorrect value in (b).

I get values different from yours and (presumably) from the book's. For (b) I get: exact probability = 0.374928, normal approx with continuity correction = 0.396911, normal approx without continuity correction = 0.472994.

RGV