Chứng minh: S= 3+3²+ 3³+ 3⁴ + 3⁵ + 3⁶ + 3⁷ + 3⁸ + 3⁹ chia hết cho (-39)

1. Mai's school is small but beautiful
2. A big yard
3. Three floors
4. There are fifty teachers in Mai's school

This is a repeation of a previous talk

L) 37.7 + 80.3 + 43.7
= 7. (37+43) + 80.3
= 7. 80 + 80 .3
= 80. (3+7)
= 80 .10
= 800
m) 113.38+113.62+87.62+87.38
= 113. (38+62) + 87. (62+38)
= 113. 100 + 87. 100
= 100. (113+87)
= 100. 200
= 20000
n)123.456+ 456.321- 256.444
= 456. (123+321)- 256.444
= 456. 444 - 256.444
= 444. (456-256)
= 444. 200
= 88800
p) 43.37+93.43+57.61+69.57
= 43. (37+93) + 57. (61+69)
= 43. 130 + 57. 130
= 130. (43+57)
= 130. 100
= 13000
q) 38.63+37.38
= 38. (63+37)
= 38. 100
= 3800

e) 12.53 + 53.172 + 53.84
= 53. (12+172+84)
= 53. 268
= 14204
g) (2100-42):21
= 2100: 21 - 42 :21
= 100 - 2
= 98
h) 39.8+60.2+21.8
= 8. (39+21) + 60.2
= 8. 60 + 60 .2
= 60 . (8+2)
= 600
i) 36.28+82.82+64.69+64.41
= 36. (28+82) + 64. (69+41)
= 36. 110 + 64. 110
= 110. (36+64)
= 110. 100
= 11000
k) 32.47+32.53
= 32. (47+53)
= 32. 100
= 3200

\(\dfrac{1}{5}=\dfrac{1\cdot7}{5\cdot7}=\dfrac{7}{35}\) ; \(\dfrac{2}{7}=\dfrac{2\cdot5}{7\cdot5}=\dfrac{10}{35}\)

số gạo còn lại chiếm số phần là:
\(\dfrac{35}{35}\) - (\(\dfrac{7}{35}+\dfrac{10}{35}\)) = \(\dfrac{18}{35}\)