Question

If the sum of the 10 terms of an A.P. is 4 times to the sum of its 5 terms, then the ratio of first term and common difference is

• A. 1 : 2
• B. 2 : 1
• C. 2 : 3
• D. 3 : 2

Answer 1

Answer: (A)

1 : 2

Answer 2

Let a be the first term and d the common difference

Then,$\frac{10}{2}\{\{ a + (10 - 1)d\} = 4 \times \frac{5}{2}\{ 2a + (5 - 1)d\}$

⇒ $2a + 9d = 4a + 8d$

⇒ $d = 2a$ ⇒ $\frac{a}{d} = \frac{1}{2}$ , ∴ a : d = 1 : 2`