Answer:
Step-by-step 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)
[tex]S_{15}=\frac{15}{2}(a_{1}+l)\\\\240=\frac{15}{2}(a_{1}+33.5)\\\\240*2=15*(a_{1}+33.5)\\\\480=15*(a_{1}+33.5)\\\\\frac{480}{15}=a_{1}+33.5\\\\32=a_{1}+33.5\\\\32-33.5=a_{1}\\-1.5=a_{1}[/tex]
a₁ = - 1.5
