Question

100 A.Ms are inserted between 20 and 80. Find the sum of first A.M and last A.M

• A. 100
• B. 80
• C. 60
• D. 92

Answer 1

The correct option is A

100

Let the common difference be d. Then the A.P will be
$20,\underset{–}{20+d},20+2d......80-2d,\underset{–}{80-d},80$
$\Rightarrow$ Sum of first and last A.M (underlined terms)
$\Rightarrow 20+d+80-d=100$