In probability distribution, if you know the formula of binomial distribution, you can find poisson distribution because poisson distribution's probability formula derive from binomial distribution's probability formula. Today, I spent more than 3 hours to learn .
This is the method of calculating seasonal variation. In ratio to trend method, we will calculate annual trend values. Then on this basis, we will calculate quarterly trend value. Now, it will be easy for us to calculate the ratio of original value to trend value which will be the seasonal .