Question

How many terms of the series 42,36, 30........amount to 150?​

Answer 1

Answer:

42,36,30....

a=42,d=-6, Sn: 150

sn=n/2{2a+ (n-1)d}

= n/2{2x42+(n-l)-6.}

= n/2{84-6n+6}

= n/2(90-6n)

150 = 45n-3n 2

50=15n-n2

n2-15n+50=0

(n-5)(n-10,)=0

n = 5

5 terms. Ans