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Tamil Nadu Board of Secondary EducationSSLC (English Medium) Class 8

A can do a piece of work in 12 hours, B and C can do it 3 hours whereas A and C can do it in 6 hours. How long will B alone take to do the same work?

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Question

A can do a piece of work in 12 hours, B and C can do it 3 hours whereas A and C can do it in 6 hours. How long will B alone take to do the same work?

Sum
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Solution

Time taken by A to complete the work = 12 hours.

∴ A’s 1 hour work = `1/12`  ...(1)

(B + C) complete the work in 3 hours.

∴ (B + C)’s 1 hour work = `1/3`  ...(2)

Add (1) and (2) 

∴ (A + B + C)’s 1 hour work = `1/12 + 1/3`

= `(1 + 4)/12`

= `5/12`

Now (A + C) complete the work in 6 hours.

∴(A + C)’s 1 hour work = `1/6`

∴ B’s 1 hour work = (A + B + C)’s 1 hour work – (A + C)’s 1 hour work

= `5/12 - 1/6`

= `(5 - 2)/12`

= `3/12`

= `1/4`

∴ B alone take 4 days to complete the work.

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Chapter 4: Life Mathematics - Exercise 4.4 [Page 150]

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Samacheer Kalvi Mathematics [English] Class 8 TN Board
Chapter 4 Life Mathematics
Exercise 4.4 | Q 6 | Page 150

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