model 4 find nth average from 1st & last number Practice Questions Answers Test with Solutions & More Shortcuts
average PRACTICE TEST [9 - 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
Question : 11 [SSC CGL Tier-I 2015]
Out of four numbers the average of the first three is 16 and that of the last three is 15. If the last number is 20 then the first number is
a) 25
b) 21
c) 28
d) 23
Answer »Answer: (d)
Let three numbers be a,b and c respectively.
∴ a + b + c = 16 × 3 = 48 ---(i)
b + c + 20 = 15 × 3 = 45
⇒ b + c = 45 – 20 = 25 ---(ii)
By equation (i) - (ii),
a = 48 – 25 = 23
Aliter : Using Rule 16,
Here, n = 3, F = 16, L = 15
l = 20, f= ?
f – l= n (F – L)
f – 20= 3 (16 – 15)
f = 3 + 20
f = 23
Question : 12
The average of 13 results is 70. The average of first seven is 65 and that of the last seven is 75, the seventh result is :
a) 70
b) 70.5
c) 68
d) 67
Answer »Answer: (a)
Seventh observation
= 65 × 7 + 7 × 75 – 13 × 70
= 455 + 525 – 910
= 980 – 910 = 70
Aliter :
Here, n = 13, x = 70
m =7, y = 65
m = 7, z = 75
Seventh result = m (y + z) – nx
= 7 (65 + 75) – 13 × 70
= 7 × (140) – 910
= 980 – 910 = 70
Question : 13 [SSC CGL 2004]
The average of 20 numbers is 12. The average of the first 12 numbers is 11 and that of the next 7 numbers is 10. The last number is :
a) 38
b) 50
c) 48
d) 40
Answer »Answer: (a)
Using Rule 1,
Average of two or more numbers/quantities is called the mean of these numbers, which is given by
$\text"Average(A)" = \text"Sum of observation / quantities"/\text"No of observation / quantities"$
∴ S = A × n
Last number = Sum of 20 numbers
– sum of first 12 numbers – sum of next 7 numbers
= 20 × 12 – 11 × 12 – 7 × 10
= 240 – 132 – 70 = 38
Question : 14
The average of six numbers is 3.95. The average of two of them is 3.4, while the average of the other two is 3.85. The average of the remaining two numbers is
a) 4.5
b) 4.7
c) 4.8
d) 4.6
Answer »Answer: (d)
Using Rule 1,
Sum of remaining two numbers
= 6 × 3.95 – 2 × 3.4 – 2 × 3.85
= 23.7 – 6.8 – 7.7 = 9.2
∴ Required average = ${9.2}/2$= 4.6
Question : 15 [SSC CHSL 2015]
The average of 12 numbers is 15 and the average of the first two is 14. What is the average of the rest?
a) 15$1/5$
b) 14$1/5$
c) 14
d) 15
Answer »Answer: (a)
Sum of remaining 10 numbers
= 12 × 15 – 2 × 14
= 180 – 28 = 152
∴ Required average =$152/10$
= $76/5$ = 15$1/5$
IMPORTANT quantitative aptitude EXERCISES
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Basic Average Questions Practice Test, Shortcuts, Tricks, PDF »
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New Average Aptitude MCQ Average of Consecutive Numbers »
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Top 99+ Average Aptitude: Twice, One Third of Numbers MCQ »
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New +99 Average Aptitude MCQ Find nth Average of Numbers »
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99+ Average Aptitude Find New Average from Error MCQ Test »
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Top 99+ Aptitude MCQ Test on Average With Excluded Number »
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Top 99+ Aptitude Average on Ages & Weights MCQ Test Quiz »
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Top Aptitude Average MCQ Find Monthly Income for Average »
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Top 149+ Aptitude Average on Cricket & Exam MCQ Test Quiz »
model 4 find nth average from 1st & last number Shortcuts »
Click to Read...model 4 find nth average from 1st & last number Online Quiz
Click to Start..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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