model 4 find nth average from 1st & last number Section-Wise Topic Notes With Detailed Explanation And Example Questions
MOST IMPORTANT quantitative aptitude - 9 EXERCISES
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The following question based on average topic of quantitative aptitude
(a) 38
(b) 50
(c) 48
(d) 40
The correct answers to the above question in:
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
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Read more find nth term Based Quantitative Aptitude Questions and Answers
Question : 1
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 : 2
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$1/5$
Question : 3
The average of the largest and smallest 3 digit numbers formed by 0, 2 and 4 would be
a) 213
b) 303
c) 222
d) 312
Answer »Answer: (d)
Largest 3–digit number formed by 0, 2 and 4 = 420 Smallest number of three digits = 204
∴ Required average
= ${420+204}/2$ = $624/2$ = 312
Question : 4
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 : 5
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 : 6
The average of three numbers is 135. The largest number is 195 and the difference between the other two is 20. The smallest number is
a) 95
b) 115
c) 105
d) 65
Answer »Answer: (a)
Using Rule 1,
According to the question,
195 + x + x + 20 = 135 × 3
⇒ 2x + 215 = 405
⇒ 2x = 405 – 215 = 190
∴ x =$190/2$ = 95
x = Smallest number
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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