The missing number questions is
a important part in SSC,ACT,SAT
and the competitive exams.
How to find missing number in a sequence?
1.Notice, if the order of number given is ascending
( smaller to larger number) or
descending ( larger to smaller number).
if the numbers increase or decrease a little
then we have the addition or subtraction
If the numbers increase or decrease a lot
then we have multiplication or division.
2.Calculate the differences between
those that are next to each other.
3. Find the pattern that applies
Find the pattern that applies
to get from one number to
the next number in the sequence.
Example Question#1: How to find missing number in a set.
Find the missing number in the following set:
5 ,17 ,29, x, 53, 65
Calculate the differences between
those that are next to each other.
17-5=12
29-17=12
65-53=12
To each number we add 12 and find the next number.
Therefore:
29+12=41
Correct answer:
41
Example Question#2: How to find missing number in a set.
Find the missing number in the following set:
8, 16, x, 64, 128, 256
Calculate the differences between
those that are next to each other.
16-8=8
128-64=64
256-128=128
We observe that to find the next number
in the series we multiply by 2.
8Χ2=16
64Χ2=128
128Χ2=256
Therefore the missing number is:
16X2=32
Answer is:
32
Example Question#3: How to find missing number in a set.
Find the missing number in the following set:
3, 10, 24, x, 108, 220
We can solve it in 2 ways.
Α way
Calculate the differences between
those that are next to each other.
10-3=7
24-10=14
108-52=56
220-108=112
The number series of the differences is:
7,14, x, 56, 112
Notice that every term is multiple by 2
7X2=14 56X2=114
The number series is GP with common ratio 2
So the number series of differences is:
7, 14, 28, 56, 112
Therefore the missing number is:
24+28=52
B way
The rule is as follows:
add 2 to the previous number then multiply times 2.
(3+2)x2=10
(10+2)x2=24
(24+2)x2=52
(52+2)x2=108
(108+2)x2=220
Correct answer is:
52
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Example Question#4: How to find missing number in a set.
Find the missing number in the following set:
9, 18, 10, 20, 12, 24, X
This is an alternating multiplication and subtracting series:
First, multiply by 2 and then subtract 8.
9X2=18 18-8=10
10X2=20 20-8=12
12X2=24
So 24-8=16
Correct answer is; 16
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Practice with selective questions that cover
the full range of number series problems
in competitive exams.
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Example Question#5: How to find missing number in a set.
Find the missing number in the following set:
8, 11, 15, 14, 17 ,15, 20, X
Explanation In this alternating repetition series,
a random number, 15, is interpolated every third number
into a simple addition series, in which each number increases by 3.
Answer is 23,15
Example Question#6: How to find missing number in a set.
Find the missing number in the following set:
8, 16, 19, 38, 41, 82, X, C
Explanation
This is an alternation multiplication and addition series.
First we multiple by 2 to go to the next term
and then add 3 to go to the next term
8x2=16 16+3=19
19x2=38 38+3=41
41x2=82 82+3=85
85x2=170
Example Question#7: How to find missing number in a set.
Find the missing number in the following set:
3, 9, 18, 54 ,108, 324, 648, X ,C
Explanation
This is an alternating multiplication series.
First we multiple by 3 and then we multiple by 2.
3x3=9 9x2=18
18x3=54 54x2=108
108x3=324 324 x2=648
648x3=1944 1944x2=3888
Answer is: 1944 , 3888
Example Question#8: How to find missing number in a set.
Find the missing number in the following set:
110, 121, X 166, 210, 265
The differences of the successive terms are:
121-110=11 210-166=44 265-210=55
The pattern of the series of differences is an Arithmetic progression with first term
11
11, 22, 33, 44, 55
So The missing number is 121 +22=133 or 133 + 33= 166
This is a two stage types series.
The terms of arithmetic progression 11,22,33,44,55 are added starting at 110
and we get the given series.
Most of the students face difficulty
while solving missing number problems
in competitive exams.
Practice with selective questions
that cover the full range of number series
problems in competitive exams.
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