a) $\frac{5}{4}$- $\frac{1}{2}$+ $\frac{-7}{8}$
b) (-$\frac{5}{24}$+ 0.75+ $\frac{7}{12}$ : (-2$\frac{1}{8}$ )
c) Tính nhanh nếu có thể $\frac{-5}{7}$ . $\frac{2}{11}$ +$\frac{-5}{7}$ .$\frac{9}{11}$+ 1$\frac{5}{7}$
a) $\frac{5}{4}$- $\frac{1}{2}$+ $\frac{-7}{8}$
b) (-$\frac{5}{24}$+ 0.75+ $\frac{7}{12}$ : (-2$\frac{1}{8}$ )
c) Tính nhanh nếu có thể $\frac{-5}{7}$ . $\frac{2}{11}$ +$\frac{-5}{7}$ .$\frac{9}{11}$+ 1$\frac{5}{7}$
Đáp án:
a) $\frac{5}{4}$ -$\frac{1}{2}$ + $\frac{-7}{8}$
= $\frac{5×2}{4×2}$ – $\frac{1×4}{2×4}$ +$\frac{-7}{8}$
=$\frac{10}{8}$- $\frac{4}{8}$+ $\frac{-7}{8}$
= $\frac{-1}{8}$
b)(-$\frac{5}{24}$ + 0,75 + $\frac{7}{12}$ ) : (-2$\frac{1}{8}$)
= (-$\frac{5}{24}$+$\frac{3×6}{4×6}$ + $\frac{7×2}{12×2}$) : $\frac{-15×3}{8×3}$
= (-$\frac{5}{24}$ + $\frac{18}{24}$ + $\frac{14}{24}$) :$\frac{-45}{24}$
= $\frac{9}{8}$ : $\frac{-45}{24}$
= $\frac{-3}{5}$
c) $\frac{-5}{7}$ .$\frac{2}{11}$ + $\frac{-5}{7}$. $\frac{9}{11}$ +1 . $\frac{5}{7}$
=$\frac{-5}{7}$ .($\frac{2}{11}$+ $\frac{9}{11}$) + $\frac{5}{7}$
= $\frac{-5}{7}$ . 1 + $\frac{5}{7}$
=0
Giải thích các bước giải:
A. 10/8 – 4/8 + (-7/8)
= -1/8
B. -5/24 + 0.75 + 7/12 : (-17/8)
= -5/24 + 18/24 + 14/24 : (-51/24)
= -5/24 + 18/24 – 14/51
= -85/408 + 306/408 – 112/408
= 109/408
C. -10/77 -45/77 + 132/77
= 77/77
=1