Question

Two angles of a polygon are right angles and the remaining are ${120}^{\circ }$ each. Find the number of sides in it.

• A. $5$
• B. $4$
• C. $3$
• D. $2$

Answer 1

The correct option is A $5$

Let number of sides of polygon is $n$.
Two angles of a polygon are right angles and the remaining are ${120}^o$ each
Sum of total angles of a polygon is = ${180}^o(n-2)$
$n=$ number of sides of polygon
Now,
$2\times {90}^o+(n-2)\times {120}^o={180}^o(n-2)$
${180}^{o}n-{120}^{o}n={180}^o+{360}^o-{240}^o$
${60}^{o}n={300}^o$
$n=5$