# Once you have a z-score, how do you calculate the value that is found in the z-tables?

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Is there a formula?

Is there a formula?

##### 1 Answer

Mar 13, 2018

Since there is no mathematical equation that can calculate the area under the normal curve between two points, there is no formula to find the probability in z-table to solve by hand. This is the reason why z-tables are provided, usually with precision of 4 decimals.

But there are formulas to calculate these probabilities at a very high precision using softwares like excel, R, and equipment like TI calculator.

In excel, are on the left of z is given by: NORM.DIST(z,0,1,true)

In TI-calculator, we can use normalcdf(-1E99, z ) to get area on the left of that z value.