若长方形的周长是80cm,两相邻的差是10cm,则长为

设宽为x厘米.
2x + 2(x + 10) = 80
2x + 2x + 20 = 80
4x = 80 - 20
4x = 60
x = 60 ÷ 4
x = 15
15 + 10 = 25cm
答：长为25cm.
算式：(80 ÷ 2 + 10) ÷ 2
= (40 + 10) ÷ 2
= 50 ÷ 2
= 25cm