Question

Câu 1:Tính

a.7/13 x 7/15 - 5/12 x 21/39 + 49/91 x 8/15

b. (12/199 + 23/200 - 34/201)  x  (1/2 - 1/3 - 1/6)

Câu 2 :Tìm x bt:

1.   0,5 + ( X - 15/2 ) : 1/2 = 9/2

2.   2012 x X - 2010 x X = 2014

3.   ( X+ 1) + ( X + 2) + ( X + 3 ) + .....+ ( X + 100 ) =5750

Ai nhanh mk tik.Thanks nhìu

Answer 1

a) \(\frac{7}{13}x\frac{7}{15}-\frac{5}{12}x\frac{21}{39}+\frac{49}{91}x\frac{8}{15}=\frac{7}{13}x\frac{7}{15}-\frac{5}{12}x\frac{7}{13}+\frac{7}{13}x\frac{8}{15}\)

\(=\frac{7}{13}x\left(\frac{7}{15}-\frac{5}{12}+\frac{8}{15}\right)=\frac{7}{13}x\left(1-\frac{5}{12}\right)=\frac{7}{13}x\frac{7}{12}=\frac{49}{156}\)

b) \(\left(\frac{12}{199}+\frac{23}{200}-\frac{34}{201}\right)x\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)=\left(\frac{12}{199}+\frac{23}{200}-\frac{34}{201}\right)x0=0\)

Answer 2

Bài 2:

a) \(0,5+\left(x-\frac{15}{2}\right):\frac{1}{2}=\frac{9}{2}\)

\(\left(x-\frac{15}{2}\right):\frac{1}{2}=4\)

\(x-\frac{15}{2}=2\) 

x = 19/2

b) \(2012\times x-2010\times x=2014\)

\(x\times\left(2012-2010\right)=2014\)

\(x\times2=2014\)

x = 1007

c) ( x + 1) + (x+2) + (x+3)+...+(x+100) = 5750

\(x\times100+\left(1+2+3+...+100\right)=5750\)

\(x\times100+5050=5750\)

\(x\times100=700\)

x = 7