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SEQUENCES AND SERIES — MATHS STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceMATHSSEQUENCES AND SERIES3 Marks
Question
150 workers were engaged to finish a job in a certain number of days 4 workers dropped out on the second day, 4 more workers dropped out on the third day and so on. It took 8 more days to finish the work. Find the number of days in which the work was completed.
✓

Answer

Given, a = 150, d = -4
$S _ { n } = \frac { n } { 2 } [ 2 \times 150 + ( n - 1 ) ( - 4 ) ]$
If total works who would have worked all n days 150(n-8)
According to question, $ \frac { n } { 2 } [ 300 + ( n - 1 ) ( - 4 ) ] = 150 ( n - 8 )$
Hence, n = 25

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