Question
Find the fourth proportional to the number:
$5, 7, 30$
$5, 7, 30$
✓
Answer
Let $x$ be the fourth proportional, then:
$5:7::30:\text{x}$
$\therefore5\times\text{x}=7\times30$
$\Rightarrow\text{x}=\frac{7\times30}{5}=7\times6$
$\text{x}=42$
$\therefore$ Fourth proportional $= 42$
$5:7::30:\text{x}$
$\therefore5\times\text{x}=7\times30$
$\Rightarrow\text{x}=\frac{7\times30}{5}=7\times6$
$\text{x}=42$
$\therefore$ Fourth proportional $= 42$
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