Question

What is chi square test write its formula.

Answer 1

Chi square test is a statistical method assessing the goodness of fit between a set of observed values and those expected theoretically.
The formula of chi square test statistic used in the chi square test is: the Chi square formula. The subscript "c" are the degrees of freedom. "O" is your observed value and "E" is your expected value.
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Answer 2

Formula for chi square test

$\chi^2c$= $\Sigma\ \frac{(O_i-E_i)^2}{E_i}$  

O (Observed value) and E (Expected value )  

Practically, a chi square test also known as Goodness to fit test is observed in the below cases

(a) For comparing the observed value and the original value (expected value) of a test.

(b) For observing the variables which are random in nature are independent or not.