Average Weight and Age Problems

The average weight of 14 students of a class is 20 kg. If a student leaves the class the average weight of the class drops by 2 kg. Find the weight of the student (in kg) who left the class.

• 43

• 49

• 45

• 46

Answer explanation

The total weight of 14 students is 14 * 20 = 280 kg. After one leaves, the average becomes 18 kg for 13 students, totaling 234 kg. The weight of the student who left is 280 - 234 = 46 kg.

The average age of 35 students of a class is 15 years, When the teacher's age is also included, then the average age increases by one year. Find the age of teacher.

• 45 years

• 51 years

• 41 years

• 35 years

Answer explanation

The total age of 35 students is 35 * 15 = 525 years. Including the teacher, the average becomes 16 years for 36 people, so total age is 36 * 16 = 576 years. Thus, the teacher's age is 576 - 525 = 51 years.

There are two sections, A and B of a class, consisting of 40 and 50 students, respectively. If the average weight of students in section A is 36 kg and that of those section B is 45 kg, then the average weight of the whole class is :

• 39 kg

• 43 kg

• 42 kg

• 41 kg

Answer explanation

To find the average weight of the whole class, calculate the total weight of both sections: (40 * 36) + (50 * 45) = 1440 + 2250 = 3690 kg. Then divide by the total number of students: 3690 / 90 = 41 kg.

Six years ago, the average age of L and M was 39 years and the average of the present ages of L, M and N is 54 years. What will be the age of N 5 years from now ?

• 97 years

• 72 years

• 92 years

• 77 years

Answer explanation

Six years ago, L and M's average age was 39, so their total age was 78. Presently, L and M are 6 years older each, totaling 90. The average age of L, M, and N is 54, so N's age is 18. In 5 years, N will be 23, making N's age 77.

Geetha, Latha and Madhuri's ages are in the ratio 5 : 6 : 3, If their average age is 42 years, then find Latha's age.

• 54 years

• 27 years

• 45 years

• 35 years

Answer explanation

The ages of Geetha, Latha, and Madhuri are in the ratio 5:6:3. Let their ages be 5x, 6x, and 3x. The average age is (5x + 6x + 3x)/3 = 42. Solving gives x = 7. Thus, Latha's age is 6x = 6*9 = 54 years.

The average weight of all children in a group is 45 kg. If 10 children of average weight 42 kg leave the group and 2 children of average weight 55 kg join the group, then the average weight of the children in the group increases by 1 14kg. The number of children in the group initially was :

• 38

• 48

• 42

• 52

Answer explanation

Let the initial number of children be x. The total weight is 45x. After 10 children leave (weight 420 kg) and 2 join (weight 110 kg), the new average is (45x - 420 + 110)/(x - 8) = 46. Solving gives x = 48.

The average of the numbers 15, 17, 20, 25, 32 and 35 is:

• 24

• 28

• 18

• 14

Answer explanation

To find the average, add the numbers: 15 + 17 + 20 + 25 + 32 + 35 = 144. Then divide by the count of numbers (6): 144 / 6 = 24. Thus, the average is 24.

The average weight of P, Q and R is 58 kg. If the average weight of P and Q is 54 kg and that of Q and R is 48 kg, then the weight of Q is:

• 26 kg

• 32 kg

• 30 kg

• 28 kg

Answer explanation

Let P, Q, R be their weights. From the averages, we have: P + Q + R = 174 kg, P + Q = 108 kg, Q + R = 96 kg. Solving these, we find Q = 30 kg.

The average weight of an apple in a sample of 10 apples was calculated as 104 g. Later on, it was found that the weighing had shown the weight of each apple 20 g less. The correct average weight of an apple in that sample is:

• 84 g

• 124 g

• 200 g

• 1240 g

Answer explanation

The initial average weight was 104 g, but each apple was actually 20 g heavier. Therefore, the correct average weight is 104 g + 20 g = 124 g. Thus, the correct average weight of an apple in the sample is 124 g.

The average weight of A, B, C, and D is 56 kg. If the average weight of A, B and C is 52 kg and that the average weight of C and D is 48 kg, then the weight of C is:

• 28 kg

• 36 kg

• 34 kg

• 30 kg

Answer explanation

Let the weights of A, B, C, and D be a, b, c, and d respectively. From the averages, we have: (a+b+c+d)/4 = 56, (a+b+c)/3 = 52, and (c+d)/2 = 48. Solving these gives c = 28 kg.