Đáp án:

 `a)31/11`

`b)2/3`

Giải thích các bước giải:

 `a)\frac{1+1/2+1/4+1/8+1/16}{1-1/2+1/4-1/8+1/16}`

`=\frac{16/16+8/16+4/16+2/16+1/16}{16/16-8/16+4/16-2/16+1/16}`

`=\frac{31/16}{11/16}`

`=31/16: 11/16`

`=31/11`

`b)\frac{5-5/3+5/9-5/27}{8-8/3+8/9-8/27}:\frac{15-15/11+\frac{15}{121}}{16-\frac{16}{11}+\frac{16}{121}}`

`=\frac{5. (1-1/3+1/9-1/27)}{8.(1-1/3+1/9-1/27)}:\frac{15.(1-1/11+\frac{1}{121})}{16.(1-\frac{1}{11}+\frac{1}{121})}`

`=5/8: 15/16`

`=5/8. 16/15`

`=\frac{5.8.2}{8.3.5}`

`=2/3`