We have seen that a number series is a grouping of numbers, that follows a particular formula or a given rule. There are several types of number series questions that occur in the IBPS and other banking exams and the Missing Number series is one of it. In the Missing Number series, a series is present with a Missing Number or asking you to predict the last term in it. The candidate has to detect and most of the times calculate the value of this Missing Number. The following article will give you many opportunities to read the concepts, get to know about the various tips and tricks and also see many examples. Let us begin.
Missing Number Series
In the Missing Number series, we see a few examples first. Sometimes, the missing number could be present in the beginning and at other times at the end of the series. As you will see this creates different difficulty levels. The strategy in the missing number series is the same as that of the wrong number series, you have to detect the rule and then use this rule to predict the next number. Following are the tips that can reduce the time consumption to some deal while trying to detect the rule that forms a number sequence:
- Pick 2/3 terms to test the rule. That means if you have, say 5 given terms, at least pick three of them to test the rule that you want to predict.
- While choosing the terms to test, select the terms that are the easiest to work with. These include terms that a factor of 2, 3, 5 or 10. Test for common rules like sum of the terms, squares, cubes and other formulae.
Let us see some examples that we shall solve. Remember the more you practice, the more you save on time.
Browse more Topics under Number Series
- Perfect Square Series
- Perfect Cube Series
- Geometric Series
- Two Stage Type Series
- Mixed Series
- Wrong Number Series
- Order and Ranking
- Decimal Fractions
- Square Roots and Cube Roots
- Simplification on BODMAS Rule
- Chain Rule
- Heights & Distances
- Odd Man Out Series
- Number Series Practice Questions
Solved Examples on Missing Number in Array of Numbers
In the following questions, a number series is given. In each series, a number is missing. The same number is present in the options below. Select the correct option:
Q 1: 32, 40, 24, 16, 24, __
A) 60 B) 12 C) 18 D) 8
Answer: Let us first detect the rule. We will check the rule on at least 2/3rd of our terms. Now let us see the first term is 32 and the third term is 24. Since the third term is smaller than the first one we can speculate that it has been obtained by a rule that has either subtraction or division involved. Similarly, the second term is got from a rule that has either addition or multiplication in it.
We see that 32 + 8 = 40 and 32 – 8 = 24. Now let us check this rule for one more term. We see that 16 + 8 = 24. Therefore this works for more than half of the given numbers. Hence the rule is correct. Therefore the missing number in the series is 16 – 8 = 8. The answer is D) 8.
Q 2: 1, 2, 6, 24, ___
A) 32 B) 64 C) 144 D) 120
Answer: The given sequence has four terms. So the rule must be correct for at least three of them. The first term is 1. The second term is 2 which can either mean 1 is added or 2 has been multiplied. the third term is 6 which can be got from 2 by multiplying it by 3. So thus far we have 1×1, 1×2, 2×3, 6×4, which works perfectly for the series. Thus the rule has been found and the last term will be 24×5 = 120. The answer is thus D) 120.
More Examples Of The Missing Term
In the following examples, a term is missing. Select the missing term from the options that have been provided below:
Q 1: ___, 12, 18, 10, 6, 14, 5, 0, 10.
A) 14 B) 15 C) 16 D) 88
Answer: This might seem intimidating at first but if you see the series carefully, you will notice that it is just like the above series if you take it in reverse. The last three numbers are all multiples of 5. Let us see what we can figure out there. From 5, the next term is 0 which can either be obtained by subtracting 5 from 5 or multiplying it by 0. The last term is 10 which can be obtained from 5 by adding it with 5. Thus we see that the last three follow the rule that [5, 5 – 5, 5 + 5]. The same rule is shown by 10. The triplet containing 10 can be written as [10, 10 -4, 10 + 4]. 10 and 5 have a difference of 5. So the first number has to be 15. Let us check if it satisfies the rule.
The first triplet can be written as 15, 15 -3, 15 + 3. Thus the rule is satisfied and the answer is B) 15.
What many people do in series questions is that they start by using the options directly in the series. This should be used as a last resort. Remember when solving a series, shorten it by selecting 2/3rd of it. In this way, you will be able to simplify a series and solve it easily, saving precious time.
In the following questions, a number series is given. All the numbers in the series are connected by a rule. one of the numbers is missing. Select the missing number of the series from the numbers given in the options below:
Q 1: 7, 16, 27, 40, ___
A) 45 B) 55 C) 50 D) 77
Ans: B) 55
Q 2: 80, 119, 166, 221, __
A) 284 B) 380 C) 264 D) 324
Ans: A) 284.