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Riya J

· started a discussion

· 1 Months ago

5/42? (Question:146796.0)

how it came

Question:
A can do a work in 7 days less than what B takes to do the work. Working together, A and B can complete the work in 8.4  days. In how many days can A alone do the work?
Options:
A) 16
B) 12
C) 14
D) 21
Solution:

Ans (c) Let A can do the work in x days.

B can do the same work in x + 7 days.

Given, \(\cfrac{1}{x}\) + \(\cfrac{1}{(x+7)}\)= \(\cfrac{5}{42}\)

\(\cfrac{x+7+x}{[x(x+7)]}\ \ =\cfrac{5}{42} \)

⇒ 5x2 + 35x = 84x + 294

⇒ 5x2 – 49x – 294 = 0

⇒ 5x2 – 70x + 21x – 294 = 0

⇒ 5x(x – 14) + (as x > 0)21 (x – 14)= 0

⇒ (x – 14)(5x + 21) = 0 ⇒ x = 14.

Knowledge Expert

· commented

· 1 Months ago

8.4=42/5.
1 day work=5/42.
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