How can I use the normal distribution table to find probabilities other than P(z<Z)?

The normal distribution tables show, for a given Z value, the probability that the random variable z takes a value less than Z or P(z<Z). This is also the area under the normal distribution curve up to Z. We'll call this area A. It is important to remember two things about the normal distribution curve: firstly that the total area under it is 1 and secondly that it is symmetrical.So if we were aiming to find P(z>Z) then we first note that this is the area under the curve from Z upwards. As the sum of the area below Z and above Z must be the total area we see that P(z<Z) + P(z>Z) = 1 and so P(z>Z) = 1-A.In dealing with negative values -Z we use the symmetry of the curve to see that the area below -Z must be equal to the area above Z, giving P(z<-Z) = P(z>Z) = 1-A from the above.Using these two facts we can find the solution to others such as P(z>-Z) or P(m<z<M).

HA
Answered by Holi A. Maths tutor

4120 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

How can I find the stationary point of y = e^2x cos x?


The point A lies on the curve with equation y = x^(1/2). The tangent to this curve at A is parallel to the line 3y-2x=1. Find an equation of this tangent at A. (PP JUNE 2015 AQA)  


Two forces P and Q act on a particle. The force P has magnitude 7 N and acts due north. The resultant of P and Q is a force of magnitude 10 N acting in a direction with bearing 120°. Find the magnitude of Q and the bearing of Q.


sin(x)/(cos(x)+1) + cos(x)/(sin(x)+1) = 1


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2026 by IXL Learning