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a ) A = 20,15 x 25,75 + 74,25 x 20,15
A = 20,15 x ( 25,75 + 74,25 )
A = 20,15 x 100
A = 2015
Tính bằng cách thuận tiện nhất
a) A = 20,15 x 25,75 + 74,25 x 20,15
= 20,15 x (25,75 + 74,25)
= 20,15 x 100
= 2015
\(=\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+...+\frac{1}{10}\)có 9 p/số
\(=\frac{1}{10}.9=\frac{9}{10}\)
\(=\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}+\)\(\frac{1}{10}\)
\(=\frac{1}{10}.9\)
\(=\frac{9}{10}\)
Đúng 100%
Đúng 100%
Đúng 100%
\(\frac{1}{10}+\frac{2}{20}+\frac{3}{30}+\frac{4}{40}+\frac{5}{50}+\frac{6}{60}+\frac{7}{70}+\frac{8}{80}+\frac{9}{90}\)
\(=\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}\)
\(=\frac{1}{10}\times9\)
\(=\frac{9}{10}\)
Ta có:
\(A=\frac{6}{5x7}+\frac{6}{7x9}+...\frac{6}{97x99}\)
\(=3x\left(\frac{2}{5x7}+\frac{2}{7x9}+...\frac{2}{97x99}\right)\)
\(=3x\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\right)\)
\(=3x\left(\frac{1}{5}-\frac{1}{99}\right)\)
\(=3x\left(\frac{99}{495}-\frac{5}{495}\right)\)
\(=3x\frac{94}{495}=\frac{94}{165}\)
Vậy \(A=\frac{94}{165}\)
\(\frac{6}{5}\)x 7 + \(\frac{6}{7}\)x 9 + .... + \(\frac{6}{97}\)x 99
= \(\frac{6}{5}\) - \(\frac{6}{7}\)+\(\frac{6}{7}\)- \(\frac{6}{9}\)+ ..... + \(\frac{6}{97}\)- \(\frac{6}{99}\)
= \(\frac{6}{5}\) - \(\frac{6}{99}\)
= \(\frac{188}{165}\)
nhớ cho đúng đó
\(2\frac{3}{4}+1\frac{5}{6}+3\frac{1}{4}+2\frac{1}{6}\)
= \(\frac{11}{4}+\frac{11}{6}+\frac{13}{4}+\frac{13}{6}\)
= \(\left(\frac{11}{4}+\frac{13}{4}\right)+\left(\frac{11}{6}+\frac{13}{6}\right)\)
= \(\frac{24}{4}+\frac{24}{6}\)
= \(6+4\)
= \(10\)
\(S.2=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\)
\(S.2=\frac{1}{1}-\frac{1}{11}\)
\(S.2=\frac{10}{11}\)
\(S=\frac{10}{11}:2\)
\(S=\frac{5}{11}\)
7/9 - 3/7 + 2/3 - 4/7
= 7/9 + 2/3 - ( 4/7 + 3/7 )
= 13/9 - 1
= 4/9
8,12 x 6 + 16,24 x 4 - 4,06 x 8
= 8,12 x 6 + 8,12 x 2 x 4 - 8,12 : 2 x 8
= 8,12 x 6 + 8,12 x 8 - 8,12 x 4
= 8,12 x ( 6 + 8 - 4 )
= 8,12 x 10
81,2
Ủng hộ nhé ! Chúc bạn học giỏi !
7/9 - 3/7 + 2/3 - 4/7
= 7/9 + 2/3 - 3/7 - 4/7
= 7/9 + 2/3 - [ 3/7 + 4/7 ]
= 13/9 - 1
= 4/9
8,12 * 6 + 16,24 * 4 - 4,06 * 8
= 8,12 * 6 + 8,12 * 2 * 4 - 4,06 * 2 * 4
= 8,12 * 6 + 8,12 * 8 - 8,12 * 4
= 8,12 * [ 6 + 8 - 4 ]
= 8,12 * 10
= 81,2
CHÚC CÁC BẠN THÀNH CÔNG . Nhớ k cho mình nhiều nhiều nhé !
a)2,5*16,27*4=(2,5*4)*16,27=10*16,27=162,7.
b)0,25*1,25*4*8=(0,25*4)*(1,25*8)=1*10=10.
d)3/4*4/5+5/6*6/7*7/8=3*4/4*5+5*6*7/6*7*8=3/5+5/8=49/40.
a) 2,5 x 16,27 x 4
= (2,5 x 4) x 16,27
= 10 x 16,27
= 162,7
b) 0,25 x 1,25 x 4 x 8
= (0,25 x 4) x (1,25 x 8)
= 1 x 10
= 10
c) 6,7 x 9,55 + 9,45 x 16,7 + 16,7
= 6,7 x 9,55 + (9,45 + 1) x 16,7
= 6,7 x 9,55 + 10,45 x 16,7
= 63,985 + 174,515
= 238,5
d) 3/4 x 4/5 + 5/6 x 6/7 x 7/8
= 3/4 x 4/5 + 5/6 x 3/4
= 3/4 x (4/5 + 5/6)
= 3/4 x 49/30
= 49/40
1/2 x (6/1-6/3+6/3-6/5+ ... +6/37-6/39)
1/2 x (6/1-6/39)
1/2 x 228/39
228/78
\(\frac{6}{1\cdot3}+\frac{6}{3.5}+\frac{6}{5.7}+...+\frac{6}{35.37}+\frac{6}{37.39}\)
\(=3\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{37}-\frac{1}{39}\right)\)
\(=3\left(1-\frac{1}{39}\right)=3\cdot\frac{38}{39}=\frac{114}{39}\)
Ps: Bạn tự rút gọn nhé!!!