三年级数学上册《求不规则图形周长》易错题 (1) 12+7+12+7 =19+12+7 =38(厘米) (2) (30+25)×2 =55×2 =110(厘米) (3) 10×4=40(厘米) (4) (9+12)×2 =21×2 =42(厘米) (5) 16×4+4×4 =64+16 =80(厘米) (6) (16+20)×2 =36×2 =72(分米) (7) 90厘米=9分米 (9+4)×2 =13×2 =26(分米) (8) (8+6)×2+2×2 =14×2+2×2 =28+4 =32(厘米) (9) 14+16+19+18 =30+19+18 =67(分米) (10) (30+10)×2+5×2 =40×2+5×2 =80+10 =90(米)