It is known that the density of gold and silver is 19.3g/cm3 and 10.5g/cm3 respectively, The results show that when the volume is 20 cm2 and the mass is 280 g, the mass of gold and silver is respectively --, --; the volume is respectively --, --

It is known that the density of gold and silver is 19.3g/cm3 and 10.5g/cm3 respectively, The results show that when the volume is 20 cm2 and the mass is 280 g, the mass of gold and silver is respectively --, --; the volume is respectively --, --

153.5g 126.47g 7.95cm2 12.05cm2

The density of substance A and substance B is 5g / cm3 and 2G / cm3 respectively, and the density after mixing is 3G / cm3. Assuming that the total volume before and after mixing remains unchanged, the total volume after mixing of substance A and substance B decreases
A.2% B.3% C.5% D.10%

The density after mixing is 3G / cm3

The density of limestone is 2.7g/cm3, P hole = 1.2%. Now the rock is broken, and the apparent density of gravel is 1.5kg/l

You're wrong. The apparent density of gravel can't be only 1.5kg/l, it should be 1.5kg/l. If you change your question to 1.5kg/l, then: remember that the density of limestone is ρ, the apparent density is ρ 0, and the bulk density is ρ 1, then: from P hole = 1 - (ρ 0 / ρ) = 1 - (ρ 0 / 2.7) = 1.2%