The average earning of a mechanic for the first 4days of a week is Rs.18 and for the last four days is Rs.22. If he earns Rs.20 on the fourth day, his average earning forthe whole week is?  Choose the correct choice from the following answers.
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 mechanic for the first 4days of a week is Rs.18 and for the last four days is Rs.22. If he earns Rs.20 on the fourth day, his average earning forthe whole week is?