9.176662186

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dễ quá em ơi nó bằng 5,243,806,989,347.97

Không cần cảm ơn chị nhé chị đang học lớp 5 hi hi

a,

36 x 40 = (36 x 4) x 10 = 144 x 10 = 1 440

72 x 60 = (72 x 6) x 10 = 432 x 10 = 4 320

89 x 50 = (89 x 5) x 10 = 445 x 10 = 4 450

b,

450 x 70 = (45 x 7) x 100 = 315 x 100 = 31 500

2300 x 500 = (23 x 5) x 10 000 = 115 x 10 000 = 1 150 000

17 000 x 30 = (17 x 3) x 10 000 = 510 000

60×20×30×40+500

120×30×40+500

3600×40+500

144000+500

144500

Trả lời 

\(20\times30\times20\times30\times40+500\)

\(=600\times600\times40+500\)

\(=360000\times40+500\)

\(=14400000+500\)

\(=14400500\)

140,280,420

140 , 280,420

Do x ⋮ 20 và x ⋮ 35 nên x ∈ BC(20; 35)

Ta có:

20 = 2².5

35 = 5.7

⇒ BCNN(20; 35) = 2².5.7 = 140

⇒ x ∈ BC(20; 35) = B(140) = {0; 140; 280; 420; ...}

Mà x < 500

⇒ x ∈ {0; 140; 280; 420}

vì x ⋮ 20 và x ⋮ 35

=> x ∈ BC(20; 35)

Ta có:

20 = 2².5           35 = 5.7

⇒ BCNN(20; 35) = 2².5.7 = 140

⇒ x ∈ BC(20; 35) = {0; 140; 280; 420; ...} 

Mà x < 500 ⇒ x ∈ {0; 140; 280; 420}

X+500=500+20

X+500=520

X=520-500

X=20

x + 500 = 500 + 20

x + 500 = 520

          x = 520 - 500

          x = 20

trao đổi k càng nhìu càng tốt nhé ^_^

ai mún mik k thì k mik trước rùi nhắn tin ai nhanh thì c người đó nếu ko thì mik k bằng nick phụ ^_^

\(20^2+x=500\)

              \(x=500-20^2\)

              \(x=500-400\)

               \(x=100\)

20^2+x=500

400+x=500

x=500-400

=100

\(\frac{1}{1\times10}+\frac{1}{2\times15}+\frac{1}{3\times20}+...+\frac{1}{98\times495}+\frac{1}{99\times500}\)

\(=\frac{1}{1\times2\times5}+\frac{1}{2\times3\times5}+\frac{1}{3\times4\times5}+...+\frac{1}{98\times99\times5}+\frac{1}{99\times100\times5}\)

\(=\frac{1}{5}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{98\times99}+\frac{1}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{100}\right)=\frac{1}{5}\times\frac{99}{100}=\frac{99}{500}\)

\(\frac{1}{1\times10}+\frac{1}{2\times15}+\frac{1}{3\times20}+...+\frac{1}{98\times495}+\frac{1}{99\times500}\)

\(=\frac{1}{1\times2\times5}+\frac{1}{2\times3\times5}+\frac{1}{3\times4\times5}+...+\frac{1}{98\times90\times5}+\frac{1}{90\times100\times5}\)

\(=\frac{1}{5}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{98\times99}+\frac{1}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(\frac{2-1}{1\times2}+\frac{3-2}{2\times3}+...+\frac{99-98}{98\times99}+\frac{100-99}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{100}\right)=\frac{99}{500}\)