John have a 630ml mixture of milk and water in the ratio 7:2. How much water must be added to make the ratio 7:3? Choose the correct choice from the following answers:
A) 40 ml  B) 60 ml  C) 70 ml  D) 80 ml  E) 90 ml
concentration of water in mixture1 =29 (since the ratio of milk and water = 7:2) ...(1)   concentration of water in pure water= 1 ...(2)   Now the above mentioned items are mixed to form mixture2 where milk and water ratio = 7 : 3   =&gt; concentration of water in mixture2 =310   By rule of alligation,   concentration of water in mixture1 (29)   concentration of water in pure water (1)   Mean concentration   (310)   1−310=710   310−29=790   =&gt; Quantity of mixture1 : Quantity of water   =710:790=110:190=1:19   Given that Quantity of mixture1 = 630 ml   =&gt; 630 : Quantity of water =1:19   =&gt; Quantity of water =630×19=70 ml   70 ml
<result>C</result>
John have a 630ml mixture of milk and water in the ratio 7:2. How much water must be added to make the ratio 7:3?