model 5 find new average from error Section-Wise Topic Notes With Detailed Explanation And Example Questions
MOST IMPORTANT quantitative aptitude - 9 EXERCISES
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Top 149+ Aptitude Average on Cricket & Exam MCQ Test Quiz »
The following question based on average topic of quantitative aptitude
(a) 72 kg
(b) 70 kg
(c) 76 kg
(d) 75 kg
The correct answers to the above question in:
Answer: (d)
Total weight increased =$1/2$ × 50 = 25 kg.
∴ Weight of the new man = 50 + 25 = 75 kg.
Aliter : Using Rule 18,The age of the new person = T + N.t.
Here, N = 50, T = 50, t = $1/2$
Weight of New boy = T + Nt
= 50 + 50 × $1/2$ = 75 kg.
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Read more new average from error Based Quantitative Aptitude Questions and Answers
Question : 1
The average weight of 20 students in a class is increased by 0.75 kg when one of the students weighing 30 kg is replaced by a new student. Weight of the new student (in kg) is :
a) 40
b) 35
c) 50
d) 45
Answer »Answer: (d)
Required answer = 30 + 20 × 0.75
= 30 kg + 15 kg = 45 kg
Aliter : Using Rule 18,
If in the group of N persons, a new person comes at the place of a person of 'T’ years, so that average age,
increases by 't’ years
Then, the age of the new person = T + N.t.
Here, N = 20, T = 30, t = 0.75
Weight of New student = T + Nt
= 30 + 20 × 0.75
= 30 + 15 = 45 kg
Question : 2
The average of 50 numbers is 38. If two numbers, namely 45 and 55 are discarded, the average of the remaining numbers is
a) 37.9
b) 37.5
c) 37.0
d) 36.5
Answer »Answer: (b)
Sum of 50 numbers = 50 × 38 = 1900
Sum of 48 numbers = 1900 – 45 – 55 = 1800
∴ Required average = $1800/48$ = 37.5
Question : 3
The average of 9 observations was found to be 35. Later on, it was detected that an observation 81 was misread as 18. The correct average of the observations is :
a) 42
b) 28
c) 45
d) 32
Answer »Answer: (a)
Correct sum of 9 observations
= 9 × 35 – 18 + 81
= 315 + 63 = 378
∴ Required correct average = $378/9$ = 42
Question : 4
The mean value of 20 observations was found to be 75, but later on it was detected that 97 was misread as 79. Find the correct mean.
a) 75.8
b) 75.7
c) 75.6
d) 75.9
Answer »Answer: (d)
Difference = 97 – 79 = 18
True average = 75 + $18/20$ = 75.9
Aliter : Using Rule 26,
If average of n numbers is m later on it was found that a number 'a’ was misread as 'b’.
The correct average will be = m +${\text"(a-b)"}/ \text"n"$.
Here, n = 20, m = 75
a = 97, b = 79
Correct mean = m + ${\text"(a - b)"}/\text"n"$
= 75 +${(97 -79)}/20$
= 75 +$18/20$
= 75 + 0.9 = 75.9
Question : 5
Mean of 10 numbers is 30. Later on it was observed that numbers 15, 23 are wrongly taken as 51, 32. The correct mean is
a) 32
b) 25.5
c) 34·5
d) 30
Answer »Answer: (b)
Difference = 15 + 23 – 51 – 32 = –45
∴ Correct average = 30 -$45/10$ = 25.5
Aliter : Using Rule 27,
The correct average = m +${\text"(a+b-p-q)"}/ \text"n"$.
Here, n = 10, m = 30
a = 15, b = 23
p = 51, q = 32
Correct Average
= m + ${\text"(a + b - p - q)"}/ \text"n"n$
= 30 + ${(15 + 23 - 51 – 32)}/10$
= 30 + $({38-83}/10)$
= 30 - $45/10$
= 30 – 4.5 = 25.5
Question : 6
The average of seven numbers is 18. If one of the number is 17 and if it is replaced by 31, then the average becomes :
a) 19.5
b) 21.5
c) 21
d) 20
Answer »Answer: (d)
Difference = 31 – 17 = 14
∴ Required average = 18 +$14/7$ = 20
Aliter : Using Rule 26,
If average of n numbers is m later on it was found that a number 'a’ was misread as 'b’.
The correct average will be = m +${\text"(a-b)"}/ \text"n"$.
Here, n = 7, m = 18
a = 31, b = 17
New Average = m + ${\text"(a - b)"}/\text"n"$
= 18 +${(31 – 17)}/7$
= 18 +$14/7$
= 18 + 2 = 20
GET average PRACTICE TEST EXERCISES
model 1 basic average questions
model 2 average of consecutive numbers
model 3 twice, thrice, one third etc. of numbers
model 4 find nth average from 1st & last number
model 5 find new average from error
model 6 find average of excluded number
model 7 average on ages/weight
model 8 find monthly income
model 9 average on cricket/exam
average Shortcuts and Techniques with Examples
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model 1 basic average questions
Defination & Shortcuts … -
model 2 average of consecutive numbers
Defination & Shortcuts … -
model 3 twice, thrice, one third etc. of numbers
Defination & Shortcuts … -
model 4 find nth average from 1st & last number
Defination & Shortcuts … -
model 5 find new average from error
Defination & Shortcuts … -
model 6 find average of excluded number
Defination & Shortcuts … -
model 7 average on ages/weight
Defination & Shortcuts … -
model 8 find monthly income
Defination & Shortcuts … -
model 9 average on cricket/exam
Defination & Shortcuts …
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