Tìm một số biết 1/5 số đó là 24
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Theo bài ra ta có,hiệu của tử và mẫu là: 24.2=48 Tử là:(210-48):2=81 Mẫu là:210-81=129 Vậy phân số cần tìm là:81/129
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Đây là toán CẤP 1, bạn không được sử dụng cách giải "Giải bài toán bằng cách lập phương trình" của chương trình lớp 8.
Giả sử số cần tìm là x. Theo đó, phép tính trên có thể được biểu diễn như sau:
(32 - x)/(24 + x) = 3/5
Để giải phương trình này, ta có thể sử dụng phương pháp giải tương đương:
5(32 - x) = 3(24 + x)
160 - 5x = 72 + 3x
8x = 88
x = 11
Vậy, số cần tìm là 11.
![](https://rs.olm.vn/images/avt/0.png?1311)
Từ đề bài ta có được các đẳng thức sau
x=24.r1+5
x=26.r2+5
r1-r2=2=>r1=r2+2
thay vào biểu thức đầu ta được
x=24.(r2+2)+5=24r2+48+5=24r2+53
=>2r2-48=0
r2=24
x=24.24+5=581
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\(\frac{1}{5}\)số đó là 24
\(\Rightarrow\)số đó là:
24 * 5 = 120
Số đó là : 24 : 1/5 = 120
Đáp số : 120