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A water tank has inlets of two types AA and BB. All inlets of type AA when open, bring in water at the same rate. All inlets of type BB, when open, bring in water at the same rate. The empty tank is completely filled in 3030 minutes if 1010 inlets of type AA and 4545 inlets of type BB are open, and in 11 hour if 88 inlets of type AA and 1818 inlets of type BB are open. In how many minutes will the empty tank get completely filled if 77 inlets of type AA and 2727 inlets of type BB are open?

Entered answer:

Solution

✅ Correct Answer: 48

We have a water tank with two types of inlets where all Type A inlets work at the same rate and all Type B inlets work at the same rate.


Let a=a = rate at which each Type A inlet fills the tank (fraction of tank per minute)

Let b=b = rate at which each Type B inlet fills the tank (fraction of tank per minute)


Scenario 1: 1010 Type A +45+ 45 Type B fill tank in 3030 minutes

Combined rate =10a+45b= 10a + 45b (fraction of tank per minute)

Since they fill 11 complete tank in 3030 minutes:

(10a+45b)×30=1(10a + 45b) \times 30 = 1

Simplifying: 10a+45b=13010a + 45b = \dfrac{1}{30} ... (1)(1)


Scenario 2: 88 Type A +18+ 18 Type B fill tank in 6060 minutes

Combined rate =8a+18b= 8a + 18b (fraction of tank per minute)

Since they fill 11 complete tank in 6060 minutes:

(8a+18b)×60=1(8a + 18b) \times 60 = 1

Simplifying: 8a+18b=1608a + 18b = \dfrac{1}{60} ... (2)(2)


Multiply equation (2)(2) by 2.52.5 to make the coefficients of bb equal:

20a+45b=2.560=12420a + 45b = \dfrac{2.5}{60} = \dfrac{1}{24} ... (3)(3)

Subtract equation (1)(1) from equation (3)(3):

(20a+45b)−(10a+45b)=124−130(20a + 45b) - (10a + 45b) = \dfrac{1}{24} - \dfrac{1}{30}

10a=5−4120=112010a = \dfrac{5-4}{120} = \dfrac{1}{120}

Therefore: a=11200a = \dfrac{1}{1200}


Substitute back into equation (2)(2):

8×11200+18b=1608 \times \dfrac{1}{1200} + 18b = \dfrac{1}{60}

1150+18b=160\dfrac{1}{150} + 18b = \dfrac{1}{60}

18b=160−1150=5−2300=110018b = \dfrac{1}{60} - \dfrac{1}{150} = \dfrac{5-2}{300} = \dfrac{1}{100}

Therefore: b=11800b = \dfrac{1}{1800}


Scenario 3: 77 Type A +27+ 27 Type B fill the tank

Combined rate =7a+27b= 7a + 27b

=7×11200+27×11800= 7 \times \dfrac{1}{1200} + 27 \times \dfrac{1}{1800}

=71200+271800= \dfrac{7}{1200} + \dfrac{27}{1800}

=71200+3200= \dfrac{7}{1200} + \dfrac{3}{200}

=71200+181200= \dfrac{7}{1200} + \dfrac{18}{1200}

=251200=148= \dfrac{25}{1200} = \dfrac{1}{48}

If the combined rate is 148\dfrac{1}{48} tanks per minute, then time to fill 11 tank =48= 48 minutes.

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