Let the volume of each contained be 100 cc.
Hence the volume of acid in each of the container =25×100,310×100&415×100 cc respectively.
The total volume of acid in the three containers =25×100+310×100+415×100=2903cc.
Similarly volume of water in each of the container =35×100,710×100&1115×100cc respectively.
So when contents of all 3 are mixed together, the total volume of water =35×100+710×100+1115×100=6103cc.
Hence, ratio of acid to water in the mixture =2903:6103=29:61