A student takes a test consisting of 100 questions with differential m...
The maximum score would be the sum of the series 9 + 13 + …. + 389 + 393 + 397 = 98 × 406/2
= 19894. Option (d) is correct.
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A student takes a test consisting of 100 questions with differential m...
Given:
- The first question is worth a certain number of marks
- Each subsequent question is worth 4 more marks than the previous question
- The third question is worth 9 marks
To find:
- The maximum score the student can obtain by attempting 98 questions
Solution:
Let's work backwards to find the maximum score.
- We know that the student is attempting 98 questions, so the last question attempted will be the 98th question. Let's call the marks for the 98th question "x".
- The second-to-last question attempted will be the 97th question, and since it is worth 4 marks less than the last question, it will be worth "x-4".
- Continuing this pattern, the first question attempted (which is worth the least amount of marks) will be worth "x - (97 x 4)".
We also know that the third question is worth 9 marks. Let's use this information to find the value of "x".
- We know that the third question is worth 9 marks and is two questions behind the last question (since there are 98 questions total and the third question is the 3rd). Therefore, the value of the last question can be expressed as:
x = 9 + (2 x 4) = 17
- Now that we know the value of the last question, we can work backwards to find the value of the first question:
x - (97 x 4) = 17
x = 17 + (97 x 4) = 405
- Therefore, the maximum score the student can obtain by attempting 98 questions is:
9 + 13 + 17 + 21 + ... + 405
This is a sum of an arithmetic sequence with a common difference of 4 and 98 terms. We can use the formula for the sum of an arithmetic sequence to find the answer:
Sum = (n/2) x (first term + last term)
Sum = (98/2) x (9 + 405)
Sum = 49 x 414
Sum = 20,286
Therefore, the correct answer is D) None of these.