甲对桌面的压强P甲= G甲 S甲 = ρV甲g S甲 =ρgh甲=2P,乙对桌面的压强P乙= G乙 S乙 = ρV乙g S乙 =ρghh乙=P.所以P甲:P乙=h甲:h乙=2P:P=2:1,所以h甲=2h乙.乙放到甲的上面,甲对地面的压强P= G甲+G乙 S甲 = ρV甲g+ρV乙g S甲 =ρgh甲+ 1 8 ρgh甲= 9 8 ρgh甲= 9 8 ×2P= 9 4 P=2.25P.故答案为:2.25P.