简便计算:90.1-9.9 （1\6+¼-1\8）×480 90.1×9.9 21+22+23+24+.+10

90.1-9.9
= 90.1 - (10 - 0.1)
= 90.1 - 10 + 0.1
= 80.2
（1\6+¼-1\8）×480
= (1/3 + 1/2 - 1/4)×240
= (1/3 + 1/4)×240
= (1/3 + 1/4)×12×20
= (4 + 3)×20
= 140
90.1×9.9
= 90.1×(10-0.1)
= 901 - 9.01
= 900 - 9 + 1 - 0.01
= 891 + 0.99
= 891.99
21+22+23+24+.+100
= (21+100) × 80 ÷ 2
= 121× 80 ÷ 2
= 121× 40
= 4840