3吨比5吨少( 40)%, (5 - 3)÷5 =40%2.5米比2米多(25 )%。(2.5 -2)÷2 =25%(62.5 )比50多25%, 50×(1+25%)=62.550比(80 )少37.5% 。 50÷(1 - 37.5%)