The average length of 6 ropes is 80 cm. If the average length of one third of the ropes measure to 70 cm, what is the average of the other ropes?	Choices.
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 ropes is 70. That means out  6 / 3= 
<gadget id="calculator"> 6 / 3</gadget>
<output>2</output>
2 ropes.   let the avg length of two ropes 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 ropes.   IMO correct option is 85..
<result>B</result>
The average length of 6 ropes is 80 cm. If the average length of one third of the ropes measure to 70 cm, what is the average of the other ropes?