Đáp án:
`-{2019}/{2020}`
Giải thích các bước giải:
`\qquad 2019/2020.(-1/5)+4/5.(-2019/2020)`
`=-{2019}/{2020}. 1/5 +4/5.(-2019/2020)`
`=-{2019}/{2020}.(1/5+4/5)`
`=-{2019}/{2020} . 1=-{2019}/{2020}`
Vậy: `2019/2020.(-1/5)+4/5.(-2019/2020)=-{2019}/{2020}`