- What is the average of first 21 multiples of 7 ?

A.) 49 B.) 77 C.) 66 D.) 57 Answer: Option 'B'

Required average = 7(1+2+....+21) / 21

(7/21)X ( (21x22) / 2 ) (because sum of first 21 natural numbers)

= 77 - In a class, the average age of 30 boys is 13 years and the average of 20 girls is 12 years. what is the average age of the whole class?

A.) 12.5 Yrs B.) 14.2 Yrs C.) 12.3 Yrs D.) 12.6 Yrs Answer: Option 'D'

Total age of 50 students

(30X 13+20 X 12) = 630

Average = 630/50 = 12.6 Years - The average age of a class of 32 students is 16 yrs. if the teacher's age is also included, the average increases by one year. Find the age of the teacher

A.) 49 B.) 48 C.) 47 D.) 50 Answer: Option 'A'

Total age of students is 32X16 = 512 Years

Total age inclusive of teacher = 33X (16+1) = 561

So, Teacher's age is 561-512 = 49 Yrs

There is a shortcut for these type of problems

Teacher's age is 16+(33X1) = 49 Years - The average of seven numbers is 18. The average of first three numbers is 14 and the average of last three numbers is 19. What is the middle number?

A.) 42 B.) 57 C.) 27 D.) None of these Answer: Option 'C'

The total of seven numbers = 7X18 = 126

The total of first 3 and last 3 numbers is = 3 X 14+3 X 19 = 99

So, the middle number is (126 - 99 ) = 27 - Average of five consecutive even numbers is 35. Find the greatest number in these five numbers?

A.) 31 B.) 33 C.) 39 D.) 36 Answer: Option 'C' - Average of 13 results is 65. If the average of first six results is 61 and average of last six results is 59 Then find the seventh result?

A.) 115 B.) 135 C.) 125 D.) 105 Answer: Option 'C' - The average weight of a class of 20 boys was calculated to be 58.4 kgs and it was later found that one weight was misread as 56 kg instead of 65 kg. What is the correct weight?

A.) 67.4kg B.) 57.75kg C.) 58.85kg D.) 49.4kg Answer: Option 'C'

Actual total weight is (20X 58.4 - 56 + 65) = 1177 Kgs

Actual average weight is 1177/20 = 58.85kgs

Students can learn and improve on their Cognitive and Mathematical Fast Calculation skills and prepare for competitive examinations like...

- All I.B.P.S and Public Sector Bank Competitive Exam
- Common Aptitude Test (CAT) Exams
- UPSC Paper-II or CSAT Exams
- SSC Competitive Exams
- Defence Competitive Exams
- L.I.C / G.I.C AO and Clerk Competitive Exams
- Railway Competitive Exam
- University Grants Commission (UGC)
- Career Aptitude Test (IT Companies) and etc.

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