How many kilograms of sugar costing Rs. 9 per kg must be mixed with 27kg of sugar costing Rs.7 per kg so that there may be gain of 10% by selling the mixture at Rs.9.24 per kg?
Answers.
A) 60 kg  B) 63 kg  C) 50 kg  D) 77 kg  E) None of these
Explanation :   Let the rate of second quality be Rs x per Kg.   Step 1 :   S.P of 1 kg of mixture = Rs. 9.24   Gain = 10%   C.P of 1 kg of mixture =[100/(100+10)×9.24].   =&gt; Rs. 8.40.   Thus, the mean price = Rs. 8.40.   Step 2 :   C.P of 1 kg of sugar of 1st kind = 900p   C.P of 1 kg of sugar of 2nd kind = 700p   Mean price = 840p   By the rule of alligation, we have:   C.P. of 1kg of C.P. of 1kg of   sugar of 1st sugar of 2nd   kind (900p) kind (700p)   \ /   Mean Price   (840p)   / \   840 - 700 : 900 - 840   (140) (60)   =&gt; Required ratio = 140 : 60 = 7 : 3.   Step 3:   Let, x kg of sugar of 1st kind be mixed with 27 kg of 2nd kind, then   =&gt;7:3=x:27.   =&gt;7/3=x/27.   =&gt;x=(7/3)x 27.   =&gt;x=63.   Answer : 63 kg
<result>B</result>
How many kilograms of sugar costing Rs. 9 per kg must be mixed with 27kg of sugar costing Rs.7 per kg so that there may be gain of 10% by selling the mixture at Rs.9.24 per kg?