MCQ
If two interior angles on the same side of a transversal intersecting two parallel lines are in the ratio $2 : 3,$ then the measure of the larger angle is:
  • A
    $54^\circ$
  • B
    $120^\circ$
  • $108^\circ$
  • D
    $136^\circ$

Answer

Correct option: C.
$108^\circ$

Let $AB$ and $CD$ are two parallel lines and $PQ$ is transverce to it.
According to question,
$\frac{\angle\text{BRS}}{\angle\text{DSR}}=\frac{2}{3}$
$\Rightarrow\ \angle\text{BRS}=\frac{2}{3}\angle\text{DSR}\dots(1)$
Now,
$\angle\text{CSR}=\angle\text{BRS} \ [$Alternate angles$]$
$\Rightarrow\ \angle\text{CSR}+\angle\text{DSR}=180^\circ$
$\Rightarrow\ \angle\text{BRS}+\angle\text{DSR}=180^\circ$
$\Rightarrow\ \frac{2}{3}\angle\text{DSR}+\angle\text{DSR}=180^\circ$
$\Rightarrow\ \angle\text{DSR}=\frac{180\times3}{5}=108^\circ$
$\Rightarrow\ \angle\text{BRS}=\frac{2}{3}\times108^\circ=72^\circ$
Thus,
$\angle\text{DSR}=108^\circ$ and $\angle\text{BRS}=72^\circ$
$\Rightarrow$ Larger angle is $\angle\text{DSR}.$

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