Type 1: Two Pipes Working Together (Both Filling) (Pipes & Cisterns)

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Q. Pipe A fills a tank in 10 hours, and Pipe B fills it in 15 hours. How long will they take to fill the tank together ?

LCM Method

[LCM of 10 and 15 : Prime Factorization: $$10=2\times 5$$ , $$15=3\times 5.$$Take each prime factor with the highest power: $$LCM=2\times 3\times 5$$ = 30. Assume the total tank capacity = 30 units.]

Work Done:

• Pipe A: $$30÷10=3\text{ units/hour}$$


• Pipe B: $$30÷15=2\text{ units/hour}$$


• Together: $$3+2=5\text{ units/hour}$$

Therefore,

Time = 30/5​ = 6 hours​

Ans: 6 hours

Trick

Combined Time = A×B​​/A+B = 10×15/10+15 ​= 150​/25 = 6 hours

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Pipes & Cisterns – TYPE 1 Practice Set

Two Pipes Working Together (Both Filling)

Q1. Pipe A fills a tank in 12 hours and Pipe B fills it in 18 hours. How long will they take together ?

(A) 6 hours  (B) 7.2 hours  (C) 8 hours  (D) 9 hours

Q2. Pipe A fills a tank in 8 hours and Pipe B fills it in 12 hours. How long will they take together ?

(A) 4 hours  (B) 4.8 hours  (C) 5 hours  (D) 6 hours

Q3. Pipe A fills a tank in 15 hours and Pipe B fills it in 10 hours. How long will they take together ?

(A) 5 hours  (B) 6 hours  (C) 7 hours  (D) 8 hours

Q4. Pipe A fills a tank in 20 hours and Pipe B fills it in 30 hours. How long will they take together ?

(A) 10 hours  (B) 12 hours  (C) 15 hours  (D) 18 hours

Q5. Pipe A fills a tank in 6 hours and Pipe B fills it in 9 hours. How long will they take together ?

(A) 3.6 hours  (B) 4 hours  (C) 4.5 hours  (D) 5 hours

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