Three pipes A, B and C can fill a tank from empty to full in 30 minutes, 20 minutes and 10 minutes respectively. When the tank is empty, all the three pipes are opened. A, B and C discharge chemical solutions P, Q and R respectively. What is the proportion of solution R in the liquid in the tank after 3 minutes?
Options:
(A) 6/18
(B) 6/11
(C) 6/68
(D) 6/19
(E) 6/12
--
Part filled by (A + B + C) in 3 minutes = 3(1/30 + 1/20 + 1/10) = 11/20
Part filled by C in 3 minutes = 3/10
Required ratio = 3/10 * 20/11 = 6/11 So the answer is: (B).
-----
A certain car uses 12 gallons of gasoline in traveling 420 miles. In order for the car to travel the same distance using 10 gallons of gasoline, by how many miles per gallon must the car’s gas mileage be increased?
Options:
(A) 2
(B) 4
(C) 6
(D) 7
(E) 10
--
420/10 = 42 The difference is 42 - 35 = 7. So the answer is: (D).
-----
How much is 25% of 40 is greater than 4/5 of 25?
Options:
(A) 10
(B) 776
(C) 66
(D) 12
(E) 99
--

(25/100) * 40 – (4/5) * 25
10 - 20 = 10 So the answer is: (A).
-----