Question
Download Solution PDFWhat is the maximum value of the sum of the numbers 36, 33, 30, 27, 24, ...?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFGiven:
The sequence is: 36, 33, 30, 27, 24, ...
We need to find the maximum value of the sum of the numbers.
This is an arithmetic progression (AP) where:
First term (a) = 36
Common difference (d) = 33 - 36 = -3
The sum of n terms of an AP is given by:
Formula used:
Sum (Sn) = \(\dfrac{n}{2}[2a + (n-1)d]\)
Calculation:
We need to find the maximum value of the sum. The AP ends when the last term becomes ≥ 0.
Last term (l) = a + (n-1)d
For the last term to be ≥ 0:
⇒ 36 + (n-1)(-3) ≥ 0
⇒ 36 - 3(n-1) ≥ 0
⇒ 36 - 3n + 3 ≥ 0
⇒ 39 - 3n ≥ 0
⇒ 3n ≤ 39
⇒ n ≤ 13
Thus, the sequence has a maximum of n = 13 terms.
Now, calculate the sum of these 13 terms:
S13 = \(\dfrac{13}{2}[2(36) + (13-1)(-3)]\)
⇒ S13 = \(\dfrac{13}{2}[72 + 12(-3)]\)
⇒ S13 = \(\dfrac{13}{2}[72 - 36]\)
⇒ S13 = \(\dfrac{13}{2}[36]\)
⇒ S13 = 13 × 18
⇒ S13 = 234
∴ The correct answer is option (3).
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