Ras Bihari, a plumber, earned on an average Rs. 925 per day in the month of January. He earned on an average Rs. 881 per day during the first 20 days and Rs. 915 per day during the last 20 days. What was his average income (in Rs.) per day from 12^th January to 20^th January?

Total earning in January = 925 × 31 = Rs. 28675
Earning of first 20 days = 881 × 20 = Rs. 17620
Earning of last 20 days = 915 × 20 = Rs. 18300
Earning of 12^th January to 20^th January = (17620 + 18300) - 28675
= 35920 - 28675
= Rs. 7245
∴ Average of earning of 12^th January to 20^th January
$$\eqalign{ & = \frac{{7245}}{9} \cr & = {\text{Rs}}{\text{. 805}} \cr} $$