Câu 3 : Tính

a) 74,15 + 4,05 : 2,5

= 74,15 + 1,62 

= 75,77

b) 100 - 2,6 x 3,9 + 20,97 

= 100 - 10,14 + 20,97 = 110,83

Câu 4: Tính nhanh

a) \(\dfrac{1}{2}\) + \(\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}\)

= 2 x (1 - 1/2 + 1/2 - 1/4 + 1/4 - 1/8 + 1/8 - 1/16 + 1/16 - 1/32 + 1/32 - 1/64)

= 2 x (1 - 1/64)

= 2 x 63/64

= 63/32

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#Toán-5

Câu 3:

a, 74,15 + 4,05 : 2,5

= 74,15 + 1,62

= 75,77

b, 100 - 2,6 x 3,9 + 20,97

= 100 - 10,14 + 20,97

= 89,86 + 20,97

= 110,83

Câu 4:

a, A =  \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\) + \(\dfrac{1}{64}\)

  2A = 1 + \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\)

2A - A = 1 + \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\) - (\(\dfrac{1}{2}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{8}\)+\(\dfrac{1}{16}\)+\(\dfrac{1}{32}\)+\(\dfrac{1}{64}\))

A = 1 +\(\dfrac{1}{2}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{8}\)+\(\dfrac{1}{16}\)+\(\dfrac{1}{32}\)-\(\dfrac{1}{2}\)-\(\dfrac{1}{4}\)-\(\dfrac{1}{8}\)-\(\dfrac{1}{16}\)-\(\dfrac{1}{32}\) - \(\dfrac{1}{64}\)

A = 1 -  \(\dfrac{1}{64}\)

=33/45+36/56+66/45=3

= 11/15 + 4/5 + 22/15 = 3

\(\dfrac{3333}{4545}+\dfrac{36}{45}+\dfrac{66}{45}=\dfrac{33}{35}+\dfrac{36}{35}+\dfrac{66}{45}=\dfrac{135}{45}=3\)

11/15+1/15+1/5=12/15+3/15=15/15=1

\(A=\frac{3333}{4545}+\frac{1}{15}+\frac{1111}{5555}\)

\(=\frac{11}{15}+\frac{1}{15}+\frac{1}{5}\)

\(=\frac{12}{15}+\frac{3}{15}\)

\(=1\)

\(A=\frac{3333}{4545}+\frac{1}{15}+\frac{1111}{5555}\)

\(=\frac{11}{15}+\frac{1}{15}+\frac{1}{5}\)

\(=\frac{12}{15}+\frac{3}{15}\)

\(=1\)

\(A=\frac{3333}{4545}+\frac{1}{15}+\frac{1111}{5555}\)

   \(=\frac{11}{15}+\frac{1}{15}+\frac{1}{5}\)

   \(=\frac{12}{15}+\frac{3}{15}\)

   \(=1\)

\(A=\frac{7}{4}.\left(\frac{33}{12}+\frac{33}{20}+\frac{33}{30}+\frac{33}{42}\right)\)

\(A=\frac{231}{4}.\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\)

\(A=\frac{231}{4}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)

\(A=\frac{231}{4}.\left(\frac{1}{3}-\frac{1}{7}\right)\)

\(A=\frac{231}{4}.\frac{4}{21}=\frac{231}{21}=11\)

k nha

\(A=\frac{7}{4}\left(\frac{33}{12}+\frac{33}{20}+\frac{33}{30}+\frac{33}{42}\right)\)

\(A=\frac{7}{4}\left(\frac{33}{3.4}+\frac{33}{4.5}+\frac{33}{5.6}+\frac{33}{6.7}\right)\)

\(A=\frac{7}{4}\left[33\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\right]\)

\(A=\frac{7}{4}\left[33\left(\frac{1}{3}-\frac{1}{7}\right)\right]\)

\(A=\frac{7}{4}\left[33\times\frac{4}{21}\right]\)

\(A=\frac{7}{4}\times\frac{44}{7}\)

\(A=11\)

Câu 1 

Ghép số lại ta được

9 + 8 + 5 + 6 - (9 + 8 + 5 + 6) = 0

Câu 2:

4 số 6 nhân lại được 6

4 số 1 nhân lại được 1

6 - 1 = 5

Câu 3:

Nhận thấy các cặp nhân đều xuất hiện các số lẻ và có chữ số 5 nên các cặp đó có tận cùng bằng 5

5 + 5 + 5 + 5 = 0

Chúc bạn học tốt !!!

\(H=\frac{7}{4}.\left(\frac{3333}{1212}+\frac{3333}{2020}+\frac{3333}{3030}+\frac{3333}{4242}\right)\)

\(H=\frac{7}{4}.3333.\left(\frac{1}{1212}+\frac{1}{2020}+\frac{1}{3030}+\frac{1}{4242}\right)\)

\(H=\frac{7}{4}.3333.\left(\frac{1}{12.101}+\frac{1}{20.101}+\frac{1}{30.101}+\frac{1}{42.101}\right)\)

\(H=\frac{7}{4}.3333.\frac{1}{101}.\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\)

\(H=\frac{7}{4}.33.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)

\(H=\frac{7}{4}.33.\left(\frac{1}{3}-\frac{1}{7}\right)\)

\(H=\frac{7}{4}.33.\left(\frac{7}{21}-\frac{3}{21}\right)\)

\(H=33.\frac{7}{4}.\frac{4}{21}\)

\(H=11.3.\frac{1}{3}\)

\(H=11\)

Tham khảo nhé~

\(H=\frac{7}{4}.\left(\frac{3333}{1212}+\frac{3333}{2020}+\frac{3333}{3030}+\frac{3333}{4242}\right)\))

\(H=\frac{7}{4}.\left(\frac{33.101}{12.101}+\frac{33.101}{20.101}+\frac{33.101}{30.101}+\frac{33.101}{42.101}\right)\)

\(H=\frac{7}{4}.\left(\frac{33}{12}+\frac{33}{20}+\frac{33}{30}+\frac{33}{42}\right)\)

\(H=\frac{7}{4}.33.\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)\)

\(H=\frac{231}{4}.\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\)

\(H=\frac{231}{4}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)

\(H=\frac{231}{4}.\left(\frac{1}{3}-\frac{1}{7}\right)\)

\(H=\frac{231}{4}.\frac{4}{21}\)

\(H=11\)

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