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The sum of 2^(nd) and 7^(th) term of an ...

The sum of `2^(nd)` and `7^(th)` term of an A.P. is 25 and that of `11^(th)` and `8^(th)` term is 75. Find the `2^(nd)` term

A

5

B

0

C

25

D

Can't be determined

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to use the properties of an Arithmetic Progression (A.P.). ### Step-by-Step Solution: 1. **Understanding the Terms of A.P.**: In an A.P., the nth term can be expressed as: \[ a_n = a + (n-1)d \] where \( a \) is the first term and \( d \) is the common difference. 2. **Setting Up the Equations**: - The 2nd term \( a_2 \) is: \[ a_2 = a + d \] - The 7th term \( a_7 \) is: \[ a_7 = a + 6d \] - According to the problem, the sum of the 2nd and 7th terms is 25: \[ a_2 + a_7 = (a + d) + (a + 6d) = 2a + 7d = 25 \quad \text{(1)} \] - The 11th term \( a_{11} \) is: \[ a_{11} = a + 10d \] - The 8th term \( a_8 \) is: \[ a_8 = a + 7d \] - According to the problem, the sum of the 11th and 8th terms is 75: \[ a_{11} + a_8 = (a + 10d) + (a + 7d) = 2a + 17d = 75 \quad \text{(2)} \] 3. **Solving the Equations**: Now we have a system of two equations: \[ 2a + 7d = 25 \quad \text{(1)} \] \[ 2a + 17d = 75 \quad \text{(2)} \] We can subtract equation (1) from equation (2): \[ (2a + 17d) - (2a + 7d) = 75 - 25 \] This simplifies to: \[ 10d = 50 \] Dividing both sides by 10 gives: \[ d = 5 \] 4. **Finding the Value of \( a \)**: Now substitute \( d = 5 \) back into equation (1): \[ 2a + 7(5) = 25 \] Simplifying this gives: \[ 2a + 35 = 25 \] Subtracting 35 from both sides: \[ 2a = 25 - 35 \] \[ 2a = -10 \] Dividing both sides by 2: \[ a = -5 \] 5. **Finding the 2nd Term**: Now we can find the 2nd term \( a_2 \): \[ a_2 = a + d = -5 + 5 = 0 \] ### Final Answer: The 2nd term of the A.P. is \( \boxed{0} \).
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