Verified answer

What you are looking for is: (treat < as <=)

P[x < 220] - P[x < 140] now we convert to N(0,1)

P[z < (220-180)/20] - P[z < (140-180)/20]

P[z < 2] - P[z < -2] where z~N(0,1)

So using the N(0,1) tables = 0.9545

The answer is 1.) 95,5%

We know that 220-180=40, which is twice the standard deviation. It is also the case that the probability of an observation from the normal distribution falling within two standard deviations from the mean (ie in the interval 140-220 here) is about 0.95. Thus the answer is 1.

corresp z values are -2 and 2

so 95.5% ... 1)