The average earning of a for the first 4days of a week is Rs18 and for the last four days is Rs20. If he earns Rs.20 on the fourth day, his average earning forthe whole week is?	Choose the correct choice.
A) Rs. 10  B) Rs. 20  C) Rs. 30  D) Rs. 40  E) Rs. 50
Total earning for the week = Sum of earning of first four days + Sum of earning of last four days - Earning of 4th day   = 4 x18 + 4 x 22 -20   = Rs. 140   ∴ Average earning = 140 / 7   = Rs. 20   Rs. 20
<result>B</result>
The average earning of a for the first 4days of a week is Rs18 and for the last four days is Rs20. If he earns Rs.20 on the fourth day, his average earning forthe whole week is?