Standard normal curve

Question

For a standard normal curve, find the area between z = 0.40 and z = 1.98. (Use 4 decimal places.)

Find the positive z value such that 80% of the standard normal curve lies between –z and z. (Use 2 decimal places.)

I do NOT understand how to find these. I struggle with the standard normal curve all the time, please help and EXPLAIN...

Answer 1

Problem 1

P(0.40<Z<1.98)

= P(Z<1.98) - P(Z<0.40)

= 0.9761 - 0.6554

= 0.3207

Problem 2

As our interval is 1-a=0.80, then the positive z-value will be at the (1-a/2)th=90th percentile. Hence, we can calculate invNorm(0.90,0,1) ≈ 1.28

Hope this helped!