Solution
I think this was rather simple. Even I could solve it! Well, on second thoughts, I did solve it but did I get it right? Here's how I did it.
The eight of us paid 30 rupees each. That totaled 240 rupees. Suppose Harish chipped in with "x" rupees, then the total amount paid was (240 + x). The average share was therefore (240 + x)/9.
Now, "x" was 20 more than the average share. Therefore, x - (240 + x)/9 = 20.
So, 9x - (240 + x) = 180.
Thus, 9x - 240 - x = 180; 8x - 240 = 180; 8x = 420. So x = 52.50.
Harish paid 52.50 rupees; the total bill amount was, therefore, 240 + 52.50 = 292.50 rupees.
Did I get it right?