The average expenditure of the hotel when there are 10 guests is Rs 60 per guests and the average ex...........

Explanation:

Let the fixed expenditure of the hotel be Rs.x and the variable expenditure ( which is dependent on the guest ) is Rs.y , then 
x + 10y = 600        ---------(1)
x + 20y = 800       ----------(2)
From (1) & (2)
10y = 200 
=>  y = Rs. 20   and    x= 400
Hence the total expenditure when there are 40 guests = 400 + 40 x 20 = 1200
Therefore,  average expenditure = 1200/40 = Rs. 30