1.2.5*32*1.25
=(2.5*4)*(8*1.25)
=10*10
=100
(0.5+1/5+1/2)/0.5
=0.5/0.5+0.2/0.5+0.5/0.5
=1+0.4+1
=2.4
(2/7+1/3)*1/13+2/3
=(6/21+7/21)*1/13+2/3
=(13/21)*1/13+2/3
=1/21+2/3
=1/21+14/21
=5/7
2.1/(4/9)+2.4*50%
=2.25+1.2
=3.45
3.设 3角的为 x张
则有 0.3x+0.5（17-x）=2.5
0.3x+8.5-0.5x=2.5
-0.2x=-6
x=30
这题是错的.