6 water pipes have an average length of 80 cm. If the average length of one third of the pipes is 70 cm, what is the average of the other pipes?
Select
A) 75.	B) 85.	C) 90.	D) 94.	E) 100.
Edit:   Given ( X1 + X2 ... + X6 ) / 6 = 80   ( X1 + X2 ... + X6 ) = 480 --&gt; Eq 1.   Now given avg length of one third pipes is 70. That means out  6 / 3= 
<gadget id="calculator"> 6 / 3</gadget>
<output>2</output>
2 pipes.   let the avg length of two pipes be ( X1 + X2 ) / 2= 70 .   ( X1 + X2 ) = 140. --&gt; eq 2.   Now we are asked to find the average of the remaining i.e. ( X3 + X4 + X5 + X6 )   Substitute eq 2 in eq 1 then we get   140 + X3 + X4 + X5 + X6 = 480   =&gt; X3 + X4 + X5 + X6 = 340   Now divide 340 by 4 we get 85.   =&gt; ( X3 + X4 + X5 + X6) / 4 = 85 = avg length of remaining pipes.   IMO correct option is 85..
<result>B</result>
6 water pipes have an average length of 80 cm. If the average length of one third of the pipes is 70 cm, what is the average of the other pipes?