一年级下册口算题大全:整十数的减法! 40-20= 50-20= 80-40= 80-50= 80-70= 90-10= 50-10= 50-20= 50-40= 90-40= 80-30= 40-20= 30-20= 80-30= 60-50= 30-20= 70-20= 90-60= 70-40= 50-30=