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Ta có:
4/5 = 4×8/5×8 = 32/40
4/6 = 4×8/6×8 = 32/48
Vậy 7 phân số vừa < 4/5 vừa > 4/6 là: 32/41; 32/42; 32/43; 32/44; 32/45; 32/46; 32/47
Rút gọn các phân số đó ta được 7 phân số thỏa mãn đề bài là: 32/41; 16/21; 32/43; 16/22; 32/45; 16/23; 32/47
ta có
\(\frac{4}{5}=\frac{28}{35}\)
\(\frac{4}{6}=\frac{28}{42}\)
vậy 7 phân số đó là:
\(\frac{28}{36};\frac{28}{37};\frac{28}{38};\frac{28}{39};\frac{28}{40};\frac{28}{41};\frac{28}{42}\)
(2+2+2):2=3
(2x2)+(2:2)=5
2x2x2-2=6
2+2+2+2=8
2x2x2+2=10
a; \(\dfrac{1}{4}\) + \(\dfrac{2}{5}\) + \(\dfrac{6}{8}\) + \(\dfrac{9}{15}\) + \(\dfrac{8}{1}\)
= (\(\dfrac{1}{4}\) + \(\dfrac{6}{8}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{9}{15}\)) + \(\dfrac{8}{1}\)
= (\(\dfrac{1}{4}\) + \(\dfrac{3}{4}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{3}{5}\)) + 8
= 1 + 1 + 8
= 2 + 8
= 10
b; \(\dfrac{1}{2}\) + \(\dfrac{2}{4}\) + \(\dfrac{3}{6}\) + \(\dfrac{4}{8}\) + \(\dfrac{5}{10}\) + \(\dfrac{6}{12}\) + \(\dfrac{7}{14}\) + \(\dfrac{8}{16}\) + \(\dfrac{10}{20}\)
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x (\(\dfrac{2}{2}\) + \(\dfrac{3}{3}\) + \(\dfrac{4}{4}\) + \(\dfrac{5}{5}\)+ \(\dfrac{6}{6}+\dfrac{7}{7}+\dfrac{8}{8}\) + \(\dfrac{10}{10}\))
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x (1 + 1 +1 + 1+ 1+ 1+ 1 +1)
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) x 1 x 8
= \(\dfrac{1}{2}\) + \(\)\(\dfrac{1}{2}\) x 8
= \(\dfrac{1}{2}\) + 4
= \(\dfrac{9}{2}\)
a; \(\dfrac{1}{4}\) + \(\dfrac{2}{5}\) + \(\dfrac{6}{8}\) + \(\dfrac{9}{15}\) + \(\dfrac{8}{1}\)
= (\(\dfrac{1}{4}\) + \(\dfrac{6}{8}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{9}{15}\)) + 8
= (\(\dfrac{1}{4}\) + \(\dfrac{3}{4}\)) + (\(\dfrac{2}{5}\) + \(\dfrac{3}{5}\)) + 8
= 1 + 1 + 8
= 2 + 8
= 10
b; \(\dfrac{1}{2}\) + \(\dfrac{2}{4}\) + \(\dfrac{3}{6}\) + \(\dfrac{4}{8}\) + \(\dfrac{5}{10}\) + \(\dfrac{6}{12}\) + \(\dfrac{7}{14}\) + \(\dfrac{8}{16}\) + \(\dfrac{9}{18}\) + \(\dfrac{10}{20}\)
= \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\)
= \(\dfrac{1}{2}\) x 10
= 5
\(\dfrac{7}{10}=0,7;\dfrac{7}{100}=0,07;6\dfrac{38}{100}=6,38;\dfrac{2014}{1000}=2,014;\dfrac{3}{2}=1,5;\dfrac{2}{5}=0,4;\dfrac{5}{8}=0,625;1\dfrac{1}{4}=1,25;6\dfrac{38}{100}=6,38\)
Câu 1: 100:25=4
Câu 2: 24+6x1/2
= 24+3
= 27
Câu 3: 1/6:6/5=5/36
Câu 4: (5/6+8/4):2
= 68/24:2
= 68/48
Câu 2: 20/10=2
Câu 6: 2/5+6/4+71/80
= 38/20+71/80
= 223/80
Câu 1:4
Câu 2:30
Câu 3:5/36
Câu 4:chưa chắc
Câu 5:2
Câu 6:chưa chắc