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What is the sum of the first 10 terms of an increasing A.P. where the first, second and fourth terms are in G.P. and the fifth term of the A.P. is 13?
  • a)
    143
  • b)
    130
  • c)
    136
  • d)
    141
Correct answer is option 'A'. Can you explain this answer?
Verified Answer
What is the sum of the first 10 terms of an increasing A.P. where the ...
Let the first term of the A.P. be 'a', and common difference be 'd'.
Then, the first, second and fourth terms of the A.P. are 'a', 'a+d' and 'a+3d' respectively.
Since, they are in G.P., (a+d)2 = a(a+3d)
=> a2+d2+2ad=a2+3ad
=> d2=ad
=> d2−ad = 0
=> d(d-a) = 0
.'. d=0 or d=a.
 Since, it is mentioned that the A.P is increasing, we will take the value of d= a.
Hence, a+4d= 13 reduces to 5a= 13 or a= 13/5=d.
Sum of first 10 terms of the A.P.= 10​/2 [2a+9d] = 5[11a] = 55a = 55 × 513​ = 143 
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Most Upvoted Answer
What is the sum of the first 10 terms of an increasing A.P. where the ...
Given:
- The first, second, and fourth terms of the A.P. are in G.P.
- The fifth term of the A.P. is 13.

To find:
- The sum of the first 10 terms of the A.P.

Approach:
1. Let the first term of the A.P be a and the common difference be d.
2. Then, the second term is a + d, and the fourth term is a + 3d.
3. Since the first, second, and fourth terms are in G.P., we can write the equation as (a + d)^2 = (a)(a + 3d).
4. Expanding and simplifying this equation, we get a^2 + 2ad + d^2 = a^2 + 3ad.
5. Simplifying further, we get 2ad + d^2 = 3ad.
6. Rearranging the terms, we have d^2 = ad.
7. Since the common difference cannot be zero, we can divide both sides of the equation by d to get d = a.
8. Substituting the value of d in the equation d^2 = ad, we get a^2 = a^2.
9. This implies that a can have any value.

Let's assume a = 1 for simplicity.

Calculation:
1. Given that the fifth term of the A.P. is 13, we can write the equation a + 4d = 13.
2. Substituting the value of a = 1, we get 1 + 4d = 13.
3. Solving this equation, we find d = 3.
4. The first ten terms of the A.P. are: 1, 4, 7, 10, 13, 16, 19, 22, 25, 28.
5. The sum of the first ten terms can be calculated using the formula for the sum of an A.P.: Sn = (n/2)(2a + (n-1)d), where Sn is the sum of the first n terms, a is the first term, and d is the common difference.
6. Substituting the values, we get S10 = (10/2)(2(1) + (10-1)3) = 5(2 + 27) = 5(29) = 145.

Therefore, the sum of the first 10 terms of the A.P. is 145, which is not one of the given options. However, since we assumed a = 1, the answer may vary depending on the value of a. Thus, none of the given options is correct.
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What is the sum of the first 10 terms of an increasing A.P. where the ...
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What is the sum of the first 10 terms of an increasing A.P. where the first, second and fourth terms are in G.P. and the fifth term of the A.P. is 13?a)143b)130c)136d)141Correct answer is option 'A'. Can you explain this answer?
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