With this normal distribution problem

900 = 750 + 2*75. In other words, 900 is 2 standard deviations away from the mean. Similarly, 975 is 3 standard deviations from the mean. So

is the random variable for the lifespan of a light bulb with the given normal distribution, and with the standard normal distribution.

We get

If you don't have a calculator/lookup table available, you can invoke the empirical rule, the one that says

The normal distribution is symmetric about its mean, so we also know

Then

0.021

Step-by-step explanation:

One way in which to approach this problem solution is to use a calculator that has statistical distribution functions built in.  My old TI-83Plus has the function "normalcdf," which does the job nicely.

Typing in normalcdf(900,975,750,75) results in the probability 0.021 that a light bulb chosen at random will last between 900 and 975 hours.

Using a table of z-scores would be a good alternative approach.  Note that the z-score corresponding to 750 hours is 0; that for 900 is +2; and that for 975 is +3.  Find the area under the standard normal curve to the left of 975 (z = 3) and that to the left of 900 (z = 2), and then subtract the two results.  It will be 0.021, as before.

the answer is 0.3175 hope that you ^w^

also you might actually want to put this picture up if you want people to solve it luckily i remember this question

stew reads at the fastest rate of 265 words per minute.

step-by-step explanation:

it's a given that felicia reads at 260 word per minute and on connie's graph we can see that she reads 200 words per minute. since stew's table tells us that he read 795 in 3 minutes, we can divide 795 by 3 to find out how many words he reads per minute.

795/3 = 265

stew reads 265 words per minute - he reads at the fastest rate since felecia reads at 260 words per minute and connie reads at 200 words per minute.

stew (265) > felecia (260) > connie (200)