If 30 oxen can plough 1/7th of a field in 2 days, how many days 18 oxen will take to do the remaining work?  Choices.
A) 30 days
B) 20 days
C) 15 days
D) 18 days
E) 21 days
Solution: We will use work equivalence method,   30/18 = (1/7)/(6/7)*x/2;   5/3 = (1/6)*x/2;   Or, x = 60/3= 
<gadget id="calculator">60/3</gadget>
<output>20</output>
20 days.   Answer: Option 20 days
<result>B</result>
If 30 oxen can plough 1/7th of a field in 2 days, how many days 18 oxen will take to do the remaining work?