Tính nhẩm:
a) \(3,25\times10\) b) \(417,56\times100\) c) \(28,5\times100\)
\(3,25\times0,1\) \(417,56\times0,01\) \(28,5\times0,01\)
Tính nhẩm:
417,56 x 100
417,56 x 0,01
417,56 x 100 = 41756
417,56 x 0,01 = 4,1756
Tính nhanh:
\(B=\dfrac{1}{1\times4}+\dfrac{1}{4\times7}+\dfrac{1}{7\times10}+...+\dfrac{1}{97\times100}\)
\(B=\dfrac{1}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{97\cdot100}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{100}\right)\)
\(=\dfrac{1}{3}\cdot\dfrac{99}{100}=\dfrac{33}{100}\)
\(3\times B=\dfrac{3}{1\times4}+\dfrac{3}{4\times7}+....+\dfrac{3}{97\times100}\)
\(3\times B=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\)
\(3\times B=1-\dfrac{1}{100}=\dfrac{99}{100}\)
\(B=\dfrac{33}{100}\)
`#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`
Tính nhẩm 417,56 x 100
Tính nhẩm 417,56 x 0,01
1. Tính nhẩm
\(2,4\times10=\)
\(1,54\times10=\)
\(3,8\times100=\)
\(1,05\times100=\)
\(4,86\times1000=\)
\(0,458\times1000=\)
2. Tính bằng cách thuận tiện
a)\(3,5\times8\times3\times1,25\)
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b)\(13,57\times4,5+13,57\times5,5\)
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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
CHO A = \(\frac{2\times9\times8+3\times12\times10+4\times15\times12+...+98\times297\times200}{2\times3\times4+3\times4\times5+4\times5\times6+...+98\times99\times100}\)
TÍNH A\(^2\)
\(A=\frac{2\cdot9\cdot8+3\cdot12\cdot10+4\cdot15\cdot12+...+98\cdot297\cdot200}{2\cdot3\cdot4+3\cdot4\cdot5+4\cdot5\cdot6+...+98\cdot99\cdot100}\)
\(=\frac{2\cdot1\cdot3\cdot3\cdot4\cdot2+3\cdot1\cdot4\cdot3\cdot5\cdot2+...+98\cdot1+99\cdot3+100\cdot2}{2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100}\)
\(=\frac{1\cdot3\cdot2\cdot\left(2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100\right)}{2\cdot3\cdot4+3\cdot4\cdot5+...+98\cdot99\cdot100}\)
\(=1\cdot3\cdot2\)
\(=6\)
\(A^2=6^2=36\)
Tính thuận tiện : 3,25:0,5+3,25:0,25+3,25:0,125-3,25:0,25
Tính bằng cách thuận tiện : 3,25 *20 + 3,25 *50+3,25 *30
3,25x20+3,25x50+3,25x30
=3,25x(20+30+50)
=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
tính nhanh
a, 13,25 : 0,125 + 13,25 : 0,25 - 3,25 : 0,5
b, 13,25 : 0,125 + 13,25 + 3,25 : 0,5