⑴ x-2/9x=21
7/9x=21
x=21÷7/9
x=21×9/7
x=27
⑵ 3/5∶6/7=x∶5/4
6/7x=3/5×5/4
6/7x=3/4
x=3/4÷6/7
x=3/4×7/6
x=7/8
⑴ 4/5-1/3X5/7+2/3÷1/3
=4/5-5/21+2/3×3
=84/105-25/105+2
= 59/105+2
=2又59/105
⑵ 35X(1-4/7+3/5)
=35-4/7×35+3/5×35
=35-20+21
=36
⑶ 628+199
=627+﹙199+1﹚
=627+200
=827
⑷ 0.47x25+76X0.47-0.47
=0.47×﹙25+76-1﹚
=0.47×100
=47