Question

If $0.75:x::5:8$, then $x$ is equal to
A. 1.12
B. 1.20
C. 1.25
D. 1.30

Answer 1

Hint:
We can write $a:b::c:d$ as $\dfrac{a}{b} = \dfrac{c}{d}$. We can simplify the equation by cross-multiplying the equation and then simplify the equation. At last, write the value of $x$ which is in fraction to decimal form.

Complete step by step solution:
We are given that $0.75:x::5:8$.
If $a:b::c:d$, then $\dfrac{a}{b} = \dfrac{c}{d}$
Then, re-writing the equation $0.75:x::5:8$ as,
$\dfrac{{0.75}}{x} = \dfrac{5}{8}$
Now, we will cross-multiply the above equation.
$8\left( {0.75} \right) = 5\left( x \right)$
On multiplying the brackets, we will get,
$5x = 6$
On dividing the equation throughout by 5, we will get,
$x = \dfrac{6}{5}$
$ \Rightarrow x = 1.20$

Hence, option B is the correct option.

Note:
The ratio $a:b$ can also be written as $\dfrac{a}{b}$. If two ratios are equal or proportional we write the proportion as $a:b::c:d$. The order of the ratio is also important, that is, \[a:b \ne b:a\]. The first number in the ratio is called antecedent and the second number in ratio is called consequent.