Tìm các phân số b/20 sao cho; 3/10<b/10<1/2 với b thuộc Z
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Bai 1: Cac phan so do la:\(\frac{5}{9}va\frac{6}{9}\)
Bai 2 : Chua hieu de Nghia la gi! T_T
Ta có : a/b=20/52 => a/20=b/52 ( hoán đổi 2 trung tỉ )
Đặt a/20=b/52=k
a/20=k => a=20k ; b/52=k => b=52k
mà BCNN(a;b)=260
=> BCNN(20k;52k)260
=> 20k + 52k= 260
=> k(20+52)=260
=> k72=260
=> k = 260:72
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Ta có: 3/10 < b/10 < 1/2
mà 1/2 = 5/10
Nên 3/10 < b/10 < 5/10
Do đó: b/10 = 4/10 suy ra b = 4
Vậy phân số b/20 là 4/20 = 1/5
\(\frac{3}{10}< \frac{b}{10}< \frac{1}{2}\)
=> \(\frac{3}{10}< \frac{b}{10}< \frac{5}{10}\)
=> \(b=4\)
* Mình thấy đề bài nó cứ kiểu gì í *