Question

How many trapeziums will be needed to make the 20th ornament in the sequence illustrated in the adjoining figure ?

• A. 82 trapeziums
• B. 80 trapeziums
• C. 78 trapeziums
• D. 86 trapeziums

Answer 1

The correct option is A 82 trapeziums

We can see the question are in $A.P.$

$a=6,d=4$

$a_n=a_1+(n-1)d$

$\Rightarrow$ $a_{20}=6+(20-1)4$

$\Rightarrow$ $a_{20}=6+\left(19\right)4$

$\Rightarrow$ $a_{20}=6+76$

$\Rightarrow$ $a_{20}=82$

$\therefore$ $82$ trapezium will be needed to make the $20th$ ornament.