Dear experts

Please help me clear my doubt.

So, the equation for covariance is like this:

But, I don't understand why sometimes the denominator (n-1) is not used. For example, my lecturer didn't put it here.

I hope you can explain when I should put it and I should not.

Thank you so much for your kind help.

Covariance Formula Cov(RA,RB)=n1in(RAiRB)(RBiRB) a. Considering the world economic outlook for the coming year and estimates of sales and earnings for the Stock A and B, you expect the rate of return for both stocks to range between 7 percent and 26 percent with the following probabilities. CovA, B=0.30(7%4.4%)(9%9.5%) =66.9 =66.9 This question comes 3 probability, so times probability for each set of AB. Thus, n1 is not applicable. RA, B=66.90/[(10.35)(12.93)]=0.50