The average marks of 13 papers is 40. The average marks of the first 7 papers are 42 and that of the last seven papers is 35. Find the marks obtained in the 7th paper.
Answers
Answer:
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Step-by-step explanation:
=>The average of 13 papers is 40, so the sum = 13 × 40 = 520
=>The average of first 7 papers is 42, so the sum will be = 7 × 42 = 294
=>The average of last 7 papers is 35, so the sum will be = 7×35 = 245
=>So, the marks obtained in the 7th paper will be = 539 – 520 = 19
follow me !
Answer: 7th paper = 19
Step-by-step explanation:
average = sum of observation / no of observation
given that for first 7 papers, average = 42
therefore
sum of marks of first seven papers = average x no of papers
sum of marks of first seven papers = 42 x 7
sum of marks of first seven papers = 294
also the sum of last 7 papers = 35 x 7
also the sum of last 7 papers = 245
total sum of first and last 7 papers (total 14 papers) = 539
sum of all 13 papers = 13 x 40
sum of all 13 papers = 520
now, in the sum of 14 papers, we have paper number
1+2+3+4...+7+7+8+9..+13, 7 repeating twice
so
1+2+3+4...+7+7+8+9..+13 = 539 ---------1
we know
1+2+3+.....+13 = 520 (found above) -----------2
subtracting 2 from 1