18．口算．
| $\frac{8}{25}$÷$\frac{4}{5}$= | 20%÷3= | $\frac{5}{12}$×$\frac{9}{10}$= | 14×$\frac{2}{7}$= | 20÷$\frac{4}{9}$= |
| $\frac{3}{4}$+$\frac{1}{2}$= | $\frac{1}{3}$-$\frac{1}{4}$= | 10-3$\frac{3}{5}$-5$\frac{2}{5}$= | $\frac{3}{5}$×$\frac{1}{4}$÷$\frac{3}{5}$×$\frac{1}{4}$= | 12×（$\frac{3}{4}$-$\frac{1}{6}$）= |
16．直接写得数：
| 3.52+0.64= | 0.35+1.9= | 2.4-1.35= | 4.22-3.6= |
| 3.4×5= | 0.25×4= | 3.2÷0.8= | 14.4÷12= |
| 5.1×0.7= | 0.6×0.13= | 0.68÷0.4= | 1.2÷5= |
13．直接写出得数
0 161372 161380 161386 161390 161396 161398 161402 161408 161410 161416 161422 161426 161428 161432 161438 161440 161446 161450 161452 161456 161458 161462 161464 161466 161467 161468 161470 161471 161472 161474 161476 161480 161482 161486 161488 161492 161498 161500 161506 161510 161512 161516 161522 161528 161530 161536 161540 161542 161548 161552 161558 161566 199269
| 3.4+7.6= | 5.3-3.8= | 10-0.56= | 5.32+6.8= |
| 5.2÷4= | 0.35×20= | 2.5×0.4= | 0.72÷0.8= |
| 1.7+0.43+3.3= | 4.5÷0.15÷2= |