Consider 100 mL of Solution 67% by weight
∴ Wt. of Solution = 100 x 1.6 = 160 g
Now suppose X g of H2O added in it Wt. of new Solution = (160 + X) g
Also volume of new Solution = (100 + X) mL
∴ Wt. of new Solution = (100 + X) x 1.2 g = (120 +1.2 X)g
∴160 +X = (120 + 1.2 X) g or X = 200 mL or 200g
∴ % by weight of new Solution