Question

Question in attachment

Answer 1

Explanation:

a₁₅ = 33.5

S₁₅ = 240

So, there are 15 terms in this arithmetic progression. So, l = a₁₅ = 33.5

Sn = (n/2)(a+l)

`S_(15)=(15)/(2)(a_(1)+l)\\\\240=(15)/(2)(a_(1)+33.5)\\\\240*2=15*(a_(1)+33.5)\\\\480=15*(a_(1)+33.5)\\\\(480)/(15)=a_(1)+33.5\\\\32=a_(1)+33.5\\\\32-33.5=a_(1)\\-1.5=a_(1)`

a₁ = - 1.5