Directions: Study the following questions carefully and answer the questions given below.
1
The average age of 36 students in a group is 14 years. When teacher's age is included the average increases by one. What is the teacher's age ?
» Explain it
C
Total age of 36 students = 14 × 36 = 504 years

Given that when teacher's age is included the average increases by one

∴  Total age along with the teacher = 15 × 37 = 555 years

Now,  the teacher's age = 555 – 504 = 51 years

Hence, option (C) is correct.
2
The average marks of a student in seven subjects was 75. His average marks in six subjects, excluding Maths, was 73. How many marks did he score in Maths ?
» Explain it
C
Total marks in seven subjecs = 7 × 75 = 525

Now,  excluding Maths

∴  Total marks in six subjects = 6 × 73 = 438

∴  Marks in Maths = 525 – 438 = 87

Hence, option (C) is correct.
3
The average age of X and Y is 33 years. If Z's age is added the average of their ages becomes 31 years. What is the age of Z ?
» Explain it
B
Total age of X and Y = 2 × 33 = 66 years

Now, Z's age is added

∴  Total age of X, Y and Z = 3 × 31 = 93 years

∴  Z's age = 93 – 66 = 27 years

Hence, option (B) is correct.
4
The average age of 12 person is 32 years. If the age of one person is added, the average decreases by one year. What is the age of the new person ?
» Explain it
A
Total age of 12 persons = 12 × 32 = 384 years

Given that if the age of one person is added, the average decreases by one year

∴  Total age of 13 persons = 13 × 31 = 403 years

Now,  age of new person = 403 – 384 = 19 years

Hence, option (A) is correct.
5
The average weight of a class of 25 students is 37 kg. When the weight of the teacher is also included, the average weight increases by 1 kg. What is the weight of the teacher ? 
» Explain it
B
Total weight of 25 students = 37 × 25 = 925 kg

Given that when the weight of the teacher is also included, the average weight increases by 1 kg

∴  Total weight along with the teacher = 38 × 26 = 988 kg

Now,  the weight of the teacher = 988 – 925 = 63 kg

Hence, option (B) is correct.