800g of a mixture of density 1.6gcm3 is made by mixing water and a liquid of density 2.5gcm3. calculate the mass of each liquid

There are 800/1.6 = 500 cm^3 of the mixture

If x grams of water were used,
1.0x + 2.5(500 - x) = 800
x = 300

1.0*300 = 300 g of water
2.5 * 200 = 500g of the heavy liquid