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a) 64,307 + 5,347 = 69,654
b) 809,3 – 25,48 = 783,82
c) 2,108 × 43 = 90,644
d) 864 ÷ 2,4 = 360
Tính:
a, 4 - \(\frac{5}{7}\)= \(\frac{23}{7}\)
b, 12 : 3 = 4
c, 578,97 x 307 = 177743,79
d, 266,22 : 34 =7,83
HOK TỐT
\(a,864 : 2,4 = 360\)
\(b, 9 : 0,25 = 36\)
\(c,108 : 22,5 = 4,8\)
a. 64 x 25 + 35 x 25 + 25
= 64 x 25 + 35 x 25 + 25 x 1
= 25 x ( 64 + 35 + 1 )
= 25 x 100
= 2500
b. 58 x 42 + 32 x 8 + 5 x 16
c. ( 42 x 43 + 57 x 43 + 43 ) - 360 : 4
= 42 x 43 + 57 x 43 + 43 x 1 - 90
= 43 x ( 42 + 57 +1 ) - 90
= 43 x 100 - 90
= 4300 - 90
= 4210
d. 456 : 2 x 181456 : 3 - 102
Trả lời:
a,\(64\times25+35\times25+25\)
\(=25\times\left(64+35+1\right)\)
\(=25\times100\)
\(=2500\)
b,\(58\times42+32\times8+5\times16\)
\(=2436+256+80\)
\(=2772\)
c,\(\left(42\times43+57\times43+43\right)-360\div4\)
\(=43\times\left(42+57+1\right)-90\)
\(=43\times100-90\)
\(=4300-90\)
\(=4210\)
d,\(456\div2\times181456\div3-102\)
\(=228\div3\times181456-102\)
\(=76\times181456-102\)
\(=13790656-102\)
\(=13790554\)
Ta có:
\(D=1.2+2.3+3.4+4.5+...+99.100\)
\(\Leftrightarrow3D=1.2.\left(3-0\right)+2.3+\left(4-1\right)+3.4+\left(5-2\right)+4.5.\left(6-3\right)+...+99.100.\left(101-98\right)\)
\(\Leftrightarrow3D=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+99.100.101-98.99.100\)
\(\Leftrightarrow3D=99.100.101\Leftrightarrow D=\frac{99.100.101}{3}=333300\)
\(B=1.3+2.4+3.5+4.6+...+99.101\)
\(\Leftrightarrow B=\left(1.3+3.5+...+99.101\right)+\left(2.4+4.6+...+98.100\right)\)
\(\Leftrightarrow6B=\left(1.3.\left(5-\left(-1\right)\right)+3.5.\left(7-1\right)+...+99.101.\left(103-97\right)\right)+\left(2.4.\left(6-0\right)+4.6.\left(8-2\right)+...+98.100.\left(102-96\right)\right)\)
\(\Leftrightarrow B=\frac{99.101.103+3}{6}+\frac{98.100.102}{6}=338250\)
Vì các bước gần tương tự như bài a) nên mình bỏ bước.
\(C=\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{48.49.50}\)
\(\Leftrightarrow C=\frac{1}{2}.\left(\frac{2}{1.2.3}+\frac{2}{2.3.4}+\frac{2}{3.4.5}+...+\frac{2}{48.49.50}\right)\)
\(\Leftrightarrow C=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+\frac{1}{3.4}-\frac{1}{4.5}+...+\frac{1}{48.49}-\frac{1}{49.50}\right)\)
\(\Leftrightarrow C=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{49.50}\right)=\frac{1}{2}.\frac{612}{1225}=\frac{306}{1225}\)
a, 64,307 + 5,347 = 69,654
b, 809,3 – 25,48 = 783,82
c, 2,108 x 43 = 90,644
d, 864 : 2,4 = 360