Question
Download Solution PDFFind the sum of given arithmetic progression 8 + 11 + 14 + 17 upto 15 terms
Answer (Detailed Solution Below)
Detailed Solution
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Formula Used:
Average = (Sum of observations)/(Number of observations)
Last term = a + (n - 1)d
Calculation:
The above series is in arithmetic progression so the middlemost term 8th term will be the average
⇒ 8th term = 8 + (8 - 1) × 3 = 29
⇒ Sum of the series = 29 × 15 = 435
∴ The sum of the above series is 435
Additional Information
We can avoid this above (29 × 15) multiplication by digit sum Method and option
The digit sum of 29 is (2 + 9) ⇒ (11) ⇒ (2) and 15 is (1 + 5) = 6
⇒ 2 × 6 = 12 ⇒ (1 + 2) ⇒ 3
Now check the options whose digit sum will be 3 there is only option 2 whose Digit sum is 3
∴ 435 is the right answer
Traditional Method:
Given:
Arithmetic progression 8 + 11 + 14 + 17 upto 15 terms
Formula Used:
Sum of arithmetic progression = n[2a + (n - 1)d]/2
Calculation:
Sum of 1st 15 terms = 15[2 × 8 + (15-1)3]/2
⇒ (15 × 58)/2
⇒ 435
∴ 435 is the right answer
Last updated on Jun 5, 2025
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