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fireagablast
1=(10/a + 45/b)(1/2)
1=(8/a + 18/b)(1)

2 =10/a + 45/b
1 = 8/a + 18/b

4 =20/a + 90/b
5 = 40/a + 90/b
..
1 = 20/a --> a=20
..
2 = 10/20+45/b--> b=30

1 = (7/20+27/30)t
t=60/75
t=12/15

12/15*60 = 48min

Hi could you explain why you've taken the equation as 10/a + 45/b and 8/a + 18/b. I am taking it as 10A+45B AND 8A+18B.. not able to get an answer though.
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Bunuel
A water tank has inlets of two types A and B. All inlets of type A when open, bring in water at the same rate. All inlets of type B, when open, bring in water at the same rate. The empty tank is completely filled in 30 minutes if 10 inlets of type A and 45 inlets of type B are open, and in 1 hour if 8 inlets of type A and 18 inlets of type B are open. In how many minutes will the empty tank get completely filled if 7 inlets of type A and 27 inlets of type B are open?

A. 40
B. 42
C. 44
D. 46
E. 48


Are You Up For the Challenge: 700 Level Questions

If we let a and b, respectively, be the number of minutes it takes a type A and a type B inlet to fill the tank completely, then 1/a and 1/b are the rates of a type A and a type B inlet, respectively. We can create the equations:

10(1/a) + 45(1/b) = 1/30 → 10/a + 45/b = 1/30

and

8(1/a) + 18(1/b) = 1/60 → 8/a + 18/b = 1/60

If we multiply the second equation by -2, we have: -16/a - 36/b = -1/30. Adding this to the first equation, we have:

-6/a + 9/b = 0

9/b = 6/a

9a = 6b

b = 9a/6 = 3a/2

Now, substitute this back to the first equation and solve for a:

10/a + 45/(3a/2) = 1/30

10/a + 90/(3a) = 1/30

Multiplying both sides by 30a, we have:

300 + 900 = a

1200 = a

Therefore, b = 3(1200)/2 = 1800.

Thus, the combined rate of 7 type A and 27 type B inlets is 7 x (1/1200) + 27 x (1/1800) = 7/1200 + 3/200 = 7/1200 + 18/1200 = 25/1200. Since time is the inverse of rate, the time is 1200/25 = 48 minutes.

Answer: E
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fireagablast
1=(10/a + 45/b)(1/2)
1=(8/a + 18/b)(1)

2 =10/a + 45/b
1 = 8/a + 18/b

4 =20/a + 90/b
5 = 40/a + 90/b
..
1 = 20/a --> a=20
..
2 = 10/20+45/b--> b=30

1 = (7/20+27/30)t
t=60/75
t=12/15

12/15*60 = 48min

Hi could you explain why you've taken the equation as 10/a + 45/b and 8/a + 18/b. I am taking it as 10A+45B AND 8A+18B.. not able to get an answer though.


Given:
1. A water tank has inlets of two types A and B.
2. All inlets of type A when open, bring in water at the same rate.
3. All inlets of type B, when open, bring in water at the same rate.
4. The empty tank is completely filled in 30 minutes if 10 inlets of type A and 45 inlets of type B are open, and in 1 hour if 8 inlets of type A and 18 inlets of type B are open.

Asked: In how many minutes will the empty tank get completely filled if 7 inlets of type A and 27 inlets of type B are open?

Let inlets A & B fill the water tank in x hours and y hours respectively

The empty tank is completely filled in 30 minutes if 10 inlets of type A and 45 inlets of type B are open

10/(2x) + 45/(2y) = 1

5/x + 45/2y = 1

The empty tank is completely filled in 1 hour if 8 inlets of type A and 18 inlets of type B are open.

8/x + 18/y = 1

5/x + 45/2y = 8/x + 18/y
3/x = 9/2y
6y = 9x
2y = 3x
y = 1.5x

8/x + 18/1.5x = 1
20/x = 1
x = 20
y = 30

In minutes will the empty tank get completely filled if 7 inlets of type A and 27 inlets of type B are open

7/20 + 27/30 = 7/20 + 9/10 = 25/20 = 5/4

Time needed = 4/5 hours = 48 minutes

IMO E
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Bunuel
A water tank has inlets of two types A and B. All inlets of type A when open, bring in water at the same rate. All inlets of type B, when open, bring in water at the same rate. The empty tank is completely filled in 30 minutes if 10 inlets of type A and 45 inlets of type B are open, and in 1 hour if 8 inlets of type A and 18 inlets of type B are open. In how many minutes will the empty tank get completely filled if 7 inlets of type A and 27 inlets of type B are open?

A. 40
B. 42
C. 44
D. 46
E. 48


Are You Up For the Challenge: 700 Level Questions

The video explains a general principle (with derivation) and 2 step method to answer the problem

Answer: Option E

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