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If a(1),a(2)a(3),….,a(15) are in A.P and...

If `a_(1),a_(2)a_(3),….,a_(15)` are in `A.P` and `a_(1)+a_(8)+a_(15)=15`, then `a_(2)+a_(3)+a_(8)+a_(13)+a_(14)` is equal to

A

`25`

B

`35`

C

`10`

D

`15`

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The correct Answer is:
To solve the problem, we need to find the value of \( a_2 + a_3 + a_8 + a_{13} + a_{14} \) given that \( a_1 + a_8 + a_{15} = 15 \) and the terms \( a_1, a_2, \ldots, a_{15} \) are in an arithmetic progression (A.P.). ### Step-by-Step Solution: 1. **Understanding A.P. Terms**: In an arithmetic progression, the \( n \)-th term can be expressed as: \[ a_n = a_1 + (n-1)d \] where \( d \) is the common difference. 2. **Finding \( a_8 \)**: The 8th term can be expressed as: \[ a_8 = a_1 + 7d \] The 15th term can be expressed as: \[ a_{15} = a_1 + 14d \] 3. **Using the Given Condition**: We know: \[ a_1 + a_8 + a_{15} = 15 \] Substituting \( a_8 \) and \( a_{15} \): \[ a_1 + (a_1 + 7d) + (a_1 + 14d) = 15 \] Simplifying this gives: \[ 3a_1 + 21d = 15 \] Dividing the entire equation by 3: \[ a_1 + 7d = 5 \quad \text{(Equation 1)} \] 4. **Finding \( a_2, a_3, a_{13}, a_{14} \)**: Now, we can express \( a_2, a_3, a_{13}, a_{14} \): \[ a_2 = a_1 + d \] \[ a_3 = a_1 + 2d \] \[ a_{13} = a_1 + 12d \] \[ a_{14} = a_1 + 13d \] 5. **Calculating the Required Sum**: We need to find: \[ a_2 + a_3 + a_8 + a_{13} + a_{14} \] Substituting the expressions: \[ (a_1 + d) + (a_1 + 2d) + (a_1 + 7d) + (a_1 + 12d) + (a_1 + 13d) \] Combining like terms: \[ 5a_1 + (1 + 2 + 7 + 12 + 13)d = 5a_1 + 35d \] 6. **Using Equation 1**: From Equation 1, we have: \[ a_1 + 7d = 5 \implies 5a_1 + 35d = 5 \cdot 5 = 25 \] 7. **Final Result**: Therefore, \[ a_2 + a_3 + a_8 + a_{13} + a_{14} = 25 \] ### Conclusion: The value of \( a_2 + a_3 + a_8 + a_{13} + a_{14} \) is \( \boxed{25} \).

To solve the problem, we need to find the value of \( a_2 + a_3 + a_8 + a_{13} + a_{14} \) given that \( a_1 + a_8 + a_{15} = 15 \) and the terms \( a_1, a_2, \ldots, a_{15} \) are in an arithmetic progression (A.P.). ### Step-by-Step Solution: 1. **Understanding A.P. Terms**: In an arithmetic progression, the \( n \)-th term can be expressed as: \[ a_n = a_1 + (n-1)d ...
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