417,56 x 100 = 41756

417,56 x 0,01 = 4,1756

\(B=\dfrac{1}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{97\cdot100}\right)\)

\(=\dfrac{1}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)

\(=\dfrac{1}{3}\left(1-\dfrac{1}{100}\right)\)

\(=\dfrac{1}{3}\cdot\dfrac{99}{100}=\dfrac{33}{100}\)

\(3\times B=\dfrac{3}{1\times4}+\dfrac{3}{4\times7}+....+\dfrac{3}{97\times100}\)

\(3\times B=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\)

\(3\times B=1-\dfrac{1}{100}=\dfrac{99}{100}\)

\(B=\dfrac{33}{100}\)

`#ava`

`B` = `frac{1}{1 × 4}` + `frac{1}{4×7}` + `frac{1}{7×10}` + ....+ `frac{1}{97×100}`

`B` = `(``frac{3}{1 × 4}` + `frac{3}{4×7}` + `frac{3}{7×10}` + ....+ `frac{3}{97×100}`)```×1/3`

`B =` `1-1/4+1/4-1/7+1/7-1/10+....+1/97 -1/100) × 1/3`

`B = (1-1/100) × 1/3`

`B= 1/3×99/100`

`B=33/100`

41756

4,1756

1 . tính nhẩm 

2,4 x 10 = 24

1,54 x 10 = 15,4

3,8 x100 = 280

1,05 x 100 = 105.

4,86 x 1000 = 4860

0,458 x 1000 = 458

1.

2,4 x 10 = 24

1,54 x 10 = 15, 4

3,8 x 100 = 380

1,05 x 100 =105

4,86 x 1000 = 4860

0, 458 x 1000 = 458

mấy bn có thể trả lời câu 2 tính bằng cách thuận tiện được ko

\(A=\frac{2\cdot9\cdot8+3\cdot12\cdot10+4\cdot15\cdot12+...+98\cdot297\cdot200}{2\cdot3\cdot4+3\cdot4\cdot5+4\cdot5\cdot6+...+98\cdot99\cdot100}\)

\(=\frac{2\cdot1\cdot3\cdot3\cdot4\cdot2+3\cdot1\cdot4\cdot3\cdot5\cdot2+...+98\cdot1+99\cdot3+100\cdot2}{2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100}\)

\(=\frac{1\cdot3\cdot2\cdot\left(2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100\right)}{2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100}\)

\(=1\cdot3\cdot2\)

\(=6\)

\(A^2=6^2=36\)

3,25x20+3,25x50+3,25x30

=3,25x(20+30+50)

=3,25x100

=325

3,25x(20+50+30)

=3,25x100

=325

3,25*20+3,25*50+3,25*30

=3,25*(20+50+30)

=3,25*100

=325

lời giải đầy đủ k mình nhé

a) 152,5

b) 125,75