Câu hỏi của Nam Nguyen

Question

a : b = 7/12

(a + 10) : b = 3/4

a + b = ?

Le Thi Khanh Huyen · Accepted Answer

$\frac{a}{b}=\frac{7}{12}\Rightarrow a=\frac{7}{12}b$

$\Rightarrow\frac{a+10}{b}=\frac{\frac{7}{12}b+10}{b}=\frac{3}{4}$

$\Rightarrow4\left(\frac{7}{12}b+10\right)=3b$

$\frac{7}{3}b+40=3b$

$3b-\frac{7}{3}b=40$

$\frac{2}{3}b=40$

$b=40.\frac{3}{2}=60$

$a=\frac{7}{12}.60=35$

$a+b=60+35=95$

Câu trả lời:

$\frac{a}{b}=\frac{7}{12}\Rightarrow a=\frac{7}{12}b$

$\Rightarrow\frac{a+10}{b}=\frac{\frac{7}{12}b+10}{b}=\frac{3}{4}$

$\Rightarrow4\left(\frac{7}{12}b+10\right)=3b$

$\frac{7}{3}b+40=3b$

$3b-\frac{7}{3}b=40$

$\frac{2}{3}b=40$

$b=40.\frac{3}{2}=60$

$a=\frac{7}{12}.60=35$

$a+b=60+35=95$

Cold Wind · Answer

$\frac{a}{b}=\frac{7}{12}\Rightarrow\frac{a}{7}=\frac{b}{12}$

Đặt $\frac{a}{7}=\frac{b}{12}=k$

$\Rightarrow a=7k$

$b=12k$

Ta có: $\frac{a+10}{b}=\frac{3}{4}$

$\Rightarrow4\left(a+10\right)=3b$

$4a+40=3b$

$\Rightarrow3b-4a=40$

$3\cdot12k-4\cdot7k=40$

$36k-28k=40$

$\left(36-28\right)k=40$

$8k=40$

$k=40:8$

$k=5$

$\Rightarrow a=7k=7\cdot5=35$

$b=12k=12\cdot5=60$

Vậy a+b= 36 + 60 = 96