A and B together can do a piece of work in 12 days. B and C together in 15 days. C and A together in 20 days. How long will A alone take to do the work? MCQ with Answer and Explanation

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A and B together can do a piece of work in 12 days. B and C together in 15 days. C and A together in 20 days. How long will A alone take to do the work?

A. 20 days

B. 60 days

C. 40 days

D. 30 days

Answer: Option D

Solution (By JKSSB Mock Tests)

2(A+B+C) = 1/12 + 1/15 + 1/20 = (5+4+3)/60 = 12/60 = 1/5 → A+B+C = 1/10. A's work = (A+B+C) - (B+C) = 1/10 - 1/15 = (3-2)/30 = 1/30. So A takes 30 days.

This question belongs to: Maths Percentage

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Question #1

25% of A = 40% of B = 1/5 of C. Find A:B:C.

A. 8:10:5

B. 10:8:5

C. 5:8:10

D. 8:5:10

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Correct Answer: Option D

Explanation:
Let 0.25A = 0.4B = 0.2C = k. Then A=4k, B=2.5k, C=5k. Multiply by 2: A:B:C = 8:5:10.

This question belongs to: Maths Percentage

Question #2

A man's salary increased by 33.33% and then decreased by 25%. His net change in salary is:

A. 10% decrease

B. No change

C. 5% decrease

D. 5% increase

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Correct Answer: Option B

Explanation:
33.33% = 1/3. Multiplier = (4/3)×(3/4)=1, no change.

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Question #3

The salary of a person was first increased by 20% and then decreased by 20%. If his original salary was Rs. 5000, what is his final salary?

A. Rs. 4600

B. Rs. 4800

C. Rs. 4900

D. Rs. 4920

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Correct Answer: Option B

Explanation:
5000 × 1.2 × 0.8 = 5000 × 0.96 = 4800.

This question belongs to: Maths Percentage

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