Average, Mixture & Alligation — Practice

Question 1

The average of 10 numbers is 45. If a number 30 is replaced by 80, the new average is:
(a) 48  (b) 50  (c) 52  (d) 55

Accepted Answer

Sum rises by 50 ⇒ average rises by 5 ⇒ 50.

Answer: (b) 50.

Question 2

20 boys average 60 kg and 30 girls average 50 kg. The class average is:
(a) 54 kg  (b) 55 kg  (c) 52 kg  (d) 56 kg

Accepted Answer

(20×60 + 30×50)/50 = 2700/50 = 54.

Answer: (a) 54 kg.

Question 3

In what ratio must milk at ₹50/L and water be mixed so the mixture costs ₹40/L?
(a) 1:4  (b) 4:1  (c) 1:5  (d) 5:1

Accepted Answer

Water(0) : Milk(50), mean 40 ⇒ water:milk = (50−40):(40−0) = 10:40 = 1:4.

Answer: (a) 1:4 (water:milk).

Question 4

A 40% acid solution and a 70% solution are mixed to get 50%. The ratio (40%:70%) is:
(a) 1:2  (b) 2:1  (c) 3:1  (d) 1:1

Accepted Answer

(70−50):(50−40) = 20:10 = 2:1.

Answer: (b) 2:1.

Question 5

From 40 L of pure milk, 8 L is removed and replaced with water, twice. Milk remaining is:
(a) 24 L  (b) 25.6 L  (c) 28 L  (d) 26 L

Accepted Answer

40 × (1 − 8/40)² = 40 × (4/5)² = 40 × 16/25 = 25.6.

Answer: (b) 25.6 L.

Question 6

The average age of a team of 11 is 22. If the captain's age is excluded, the average of the rest is 21. The captain's age is:
(a) 30  (b) 32  (c) 33  (d) 31

Accepted Answer

Total = 11×22 = 242; rest = 10×21 = 210; captain = 242 − 210 = 32.

Answer: (b) 32.

Practice — Average, Mixture & Alligation

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