\(=\dfrac{1}{5}+\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{5}-\dfrac{1}{5}-\dfrac{1}{5}=0\)

( chỉ cần rút gọn đến phân số tối giản của từng số là sẽ ra )

5 × 8 – 20 = 40 – 20 = 20

5 × 4  + 8 = 20 + 8 = 28

4 × 7 – 18 = 28 – 18 = 10.

Lời giải:

$\frac{15}{8}: \frac{5}{20}-\frac{7}{8}: \frac{1}{4}$

$=\frac{15}{8}: \frac{1}{4}-\frac{7}{8}: \frac{1}{4}$

$=(\frac{15}{8}-\frac{7}{8}): \frac{1}{4}$

$=\frac{8}{8}: \frac{1}{4}=1\times 4=4$

\(\dfrac{15}{8}\): \(\dfrac{5}{20}\) - \(\dfrac{7}{8}\): \(\dfrac{1}{4}\)

= \(\dfrac{15}{8}\): \(\dfrac{1}{4}\) - \(\dfrac{7}{8}\): \(\dfrac{1}{4}\)

= ( \(\dfrac{15}{8}\) - \(\dfrac{7}{8}\)) : \(\dfrac{1}{4}\)

= \(\dfrac{8}{8}\) : \(\dfrac{1}{4}\)

= 1 \(\times\) \(\dfrac{4}{1}\)

= 4

a) 15 . (27 + 18 + 6 ) + 15 . ( 23 +12 ) =  15. 51 + 15 . 35 = 765 + 525 = 1290

b) 14 . 35 . 5 + 10 . 25 . 7 + 20 . 70 = 2450 + 1750 + 1400 = 2452450

c) 53 . ( 51 + 4 ) + 53 . ( 49  + 96 ) + 53 = 53 . 55 + 53 . 145 + 53 = 2915 . 7685 = 22401775

d) 46 . ( 27 +75 ) +8 . ( 58 + 25 ) + 8 . ( 58 + 25 ) . 2 = 46 . 102 + 8 . 83 + 8 . 83 =  4692 + 664 + 664 = 6020

1) \(\left(+15\right)+\left(+17\right)=15+17=32\)

2) \(\left(-3\right)+\left(-7\right)=-3-7=-\left(3+7\right)=-10\)

3) \(\left(-25\right)+\left(+4\right)=-25+4=-\left(25-4\right)=-21\)

4) \(\left(-6\right)+\left(-54\right)=-6-54=-\left(6+54\right)=-60\)

5) \(\left(-15\right)+20=20-15=5\)

6) \(\left(-5\right)+8+7+5\)

\(=\left(-5+5\right)+\left(8+7\right)\)

\(=15\)

7) \(\left(-8\right)+\left(-11\right)+\left(-2\right)\)

\(=\left[\left(-8\right)+\left(-2\right)\right]+\left(-11\right)\)

\(=\left(-10\right)+\left(-11\right)\)

\(=-21\)

8) \(15+\left(-5\right)+\left(-14\right)+\left(-16\right)\)

\(=\left[15+\left(-5\right)\right]+\left[\left(-14\right)+\left(-16\right)\right]\)

\(=10+\left(-30\right)\)

\(=-20\)

9) \(\left(-20\right)+\left(-14\right)+3+\left(-86\right)\)

\(=\left[\left(-20\right)+3\right]+\left[\left(-14\right)+\left(-86\right)\right]\)

\(=\left(-17\right)+\left(-100\right)\)

\(=-117\)

10) \(\left(-136\right)+123+\left(-264\right)+\left(-83\right)+240\)

\(=\left[\left(-136\right)+\left(-264\right)\right]+\left[123+\left(-83\right)\right]+240\)

\(=\left(-400\right)+40+240\)

\(=\left(-360\right)+240\)

\(=-120\)

11) \(\left(-596\right)+2001+1999+\left(-404+189\right)\)

\(=\left(-596\right)+2001+1999-404+189\)

\(=\left[\left(-596\right)-404\right]+\left(2001+189\right)+1999\)

\(=\left(-1000\right)+2190+1999\)

\(=1190+1999\)

\(=3189\)

12) \(314+\left(-153\right)+64+121+\left(-247\right)+218\)

\(=\left(314+64+121\right)+\left[\left(-153\right)+\left(-247\right)\right]+218\)

\(=\left(378+121\right)+\left(-400\right)+218\)

\(=499-400+218\)

\(=99+218\)

\(=317\)

\(\text{#}Toru\)