1.tính
a, ($\frac{-1}{31}$ ) × $\frac{13}{76}$ +$\frac{1}{31}$ × $\frac{86}{76}$ +$\frac{3}{5}$
b, $\frac{1}{9}$ × $\frac{7}{15}$ +$\frac{7}{15}$ × $\frac{8}{9}$ +$\frac{4}{7}$
1.tính
a, ($\frac{-1}{31}$ ) × $\frac{13}{76}$ +$\frac{1}{31}$ × $\frac{86}{76}$ +$\frac{3}{5}$
b, $\frac{1}{9}$ × $\frac{7}{15}$ +$\frac{7}{15}$ × $\frac{8}{9}$ +$\frac{4}{7}$
Đáp án:
b, 1/9 x 7/15 + 7/15 x 8/9 + 4/7
= (1/9 + 8/9) x 7/15 + 4/7
= 1 x 7/15 + 4/7
= 7/15 + 4/7
= 49/105 + 60/105
= 109/105
a -1/31 . 13/76 + 1/31 . 86/76 + 3/5
= 1/31 . -13/76 + 1/13 . 86/76 + 3/5
= 1/31 . ( -13/76 + 1/13 ) + 3/5
= 1/31 . -96/988 + 3/5
= 1/31 . -24/247 + 3/5
= -24/7657 + 3/5
= 22851/38285
Giải thích các bước giải:
a, …..
b, 1/9 x 7/15 + 7/15 x 8/9 + 4/7
= (1/9 + 8/9) x 7/15 + 4/7
= 1 x 7/15 + 4/7
= 7/15 + 4/7
= 49/105 + 60/105
= 109/105
* Xin lỗi bn, mik ko bt làm phần a !