จงหาค่าของตัวแปรในสัดส่วนที่กำหนดให้ในแต่ละข้อต่อไปนี้
1) \(\mathtt{\dfrac{x}{20} = \dfrac{4}{5}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{x}{20}} &= \mathtt{\frac{4}{5}} \\
\mathtt{x} &= \mathtt{\frac{4}{5}} \times \mathtt{20} \\
\mathtt{x} &= \mathtt{16}
\end{align}\)
\mathtt{\frac{x}{20}} &= \mathtt{\frac{4}{5}} \\
\mathtt{x} &= \mathtt{\frac{4}{5}} \times \mathtt{20} \\
\mathtt{x} &= \mathtt{16}
\end{align}\)
ตอบ x = 16
2) \(\mathtt{\dfrac{y}{9} = \dfrac{8}{12}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{y}{9}} &= \mathtt{\frac{8}{12}} \\
\mathtt{y} &= \mathtt{\frac{8}{12}} \times \mathtt{9} \\
\mathtt{y} &= \mathtt{6}
\end{align}\)
\mathtt{\frac{y}{9}} &= \mathtt{\frac{8}{12}} \\
\mathtt{y} &= \mathtt{\frac{8}{12}} \times \mathtt{9} \\
\mathtt{y} &= \mathtt{6}
\end{align}\)
ตอบ y = 6
3) \(\mathtt{\dfrac{3}{9} = \dfrac{1}{b}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{3}{9}} &= \mathtt{\frac{1}{b}} \\
\mathtt{3b} &= \mathtt{1 \times 9} \\
\mathtt{b} &= \mathtt{\frac{9}{3}} \\
\mathtt{b} &= \mathtt{3}
\end{align}\)
\mathtt{\frac{3}{9}} &= \mathtt{\frac{1}{b}} \\
\mathtt{3b} &= \mathtt{1 \times 9} \\
\mathtt{b} &= \mathtt{\frac{9}{3}} \\
\mathtt{b} &= \mathtt{3}
\end{align}\)
ตอบ b = 3
4) \(\mathtt{\dfrac{10}{3} = \dfrac{m}{9}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{10}{3}} &= \mathtt{\frac{m}{9}} \\
\mathtt{\frac{10}{3} \times 9} &= \mathtt{m} \\
\mathtt{30} &= \mathtt{m}
\end{align}\)
\mathtt{\frac{10}{3}} &= \mathtt{\frac{m}{9}} \\
\mathtt{\frac{10}{3} \times 9} &= \mathtt{m} \\
\mathtt{30} &= \mathtt{m}
\end{align}\)
ตอบ m = 30
5) \(\mathtt{\dfrac{5}{m} = \dfrac{35}{49}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{5}{m}} &= \mathtt{\frac{35}{49}} \\
\mathtt{5 \times 49} &= \mathtt{35m} \\
\mathtt{\frac{5 \, \times \, 49}{35}} &= \mathtt{m} \\
\mathtt{7} &= \mathtt{m}
\end{align}\)
\mathtt{\frac{5}{m}} &= \mathtt{\frac{35}{49}} \\
\mathtt{5 \times 49} &= \mathtt{35m} \\
\mathtt{\frac{5 \, \times \, 49}{35}} &= \mathtt{m} \\
\mathtt{7} &= \mathtt{m}
\end{align}\)
ตอบ m = 7
6) \(\mathtt{\dfrac{1}{a} = \dfrac{5}{16}}\)
วิธีทำ
\(\begin{align}
\mathtt{\frac{1}{a}} &= \mathtt{\frac{5}{16}} \\
\mathtt{1 \times 16} &= \mathtt{5a} \\
\mathtt{\frac{16}{5}} &= \mathtt{a}
\end{align}\)
\mathtt{\frac{1}{a}} &= \mathtt{\frac{5}{16}} \\
\mathtt{1 \times 16} &= \mathtt{5a} \\
\mathtt{\frac{16}{5}} &= \mathtt{a}
\end{align}\)
ตอบ a = \(\mathtt{\dfrac{16}{5}}\)