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Lời giải:
$1+2+3+....+25$
$=(1+25)+(2+24)+(3+23)+(4+22)+(5+21)+(6+20)+(7+19)+(8+18)+(9+17)+(10+16)+(11+15)+(12+14)+13$
$=\underbrace{26+26+26+...+26}_{12}+13$
$=26\times 12+13=325$
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9/14 .<.. 11/14 4/25 .<.. 4/23 5/6 ..<. 7/8 1 ..>. 14/15
8/9 ..=. 24/27 20/19 ..>. 20/27 8/7 .>.. 9/8 1 .<..15/14
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a,13/15+12/20+17/23 b,7/4+5/4+9/8+3/2
=(13/15+12/20)+17/23 =12/4+(9/8+3/2)
=(52/60+36/60)+17/23 =3+(9/8+12/8)
=88/60+17/23=22/15+17/23 =3+21/8=3/1+21/8
=506/345+255/345=761/345 =24/8+21/8=45/8
Nghe nói bạn đang cần gấp thế mà gửi muộn mong bạn thông cảm
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1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+34+25+26+27+28+29+30=475
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a, =(5+40)+(8+37)+(11+34)+(14+31)+(17+28)+(20+23)
= 45 + 45 + 45 + 45 + 45 + 43
= 90 + 90 + 83
= 180 + 83
= 263
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Lời giải:
$\frac{15}{8}: \frac{5}{20}-\frac{7}{8}: \frac{1}{4}$
$=\frac{15}{8}: \frac{1}{4}-\frac{7}{8}: \frac{1}{4}$
$=(\frac{15}{8}-\frac{7}{8}): \frac{1}{4}$
$=\frac{8}{8}: \frac{1}{4}=1\times 4=4$
\(\dfrac{15}{8}\): \(\dfrac{5}{20}\) - \(\dfrac{7}{8}\): \(\dfrac{1}{4}\)
= \(\dfrac{15}{8}\): \(\dfrac{1}{4}\) - \(\dfrac{7}{8}\): \(\dfrac{1}{4}\)
= ( \(\dfrac{15}{8}\) - \(\dfrac{7}{8}\)) : \(\dfrac{1}{4}\)
= \(\dfrac{8}{8}\) : \(\dfrac{1}{4}\)
= 1 \(\times\) \(\dfrac{4}{1}\)
= 4
=7/4 đúng ko bạn