Given, i=1∑nai=192
a1+a2⋯an=192
⇒2n(a1+an)=192
a1+an=n384⋯(1)
Also given i=1∑2na2i=120
⇒2nterms⏟a2+a4+a6⋯an=120
⇒2n×21[a2+an]=120
a2+an=n480
a1+1+an=n480⋯(2)
Now equation (2)−equation (1)
n480−n384=(a1+an+1)−(a,+an)
n1(480−384)=1
480−384=n
n=96