If A = 1 – 10 + 3 – 12 + 5 – 14 + 7 + ... upto 60 terms, then what is the value of A?

Question

নিচের অপশন গুলা দেখুন

• – 240
• – 310
• – 360
• – 270

Answer 1

সঠিক উত্তর হচ্ছে: – 270

ব্যাখ্যা: Divide the given series into two parts,
⇒ A = (1 + 3 + 5 + 7 + 9 + 11 + ….. up to 30th term) - (10 + 12 + 14 + 16 + 18 + …. up to 30th term)
Sum of the series = [(number of terms(n))/2] × [2 × first term(a) + (n - 1)d]
⇒ A = {30/2 × [2 × 1 + (30 - 1) × 2]} - {30/2 × [2 × 10 + (30 - 1) × 2}
⇒ A = 900 - 1170
∴ A = -270