Practice Test: Number Series- 2 - CAT MCQ

The series is 14, 28, 20, 40, 32, 64
Take three terms at a time. The notation be as follows:-
Let, First term = a = 14
It is evident that Second term= 2*a = 2 * 14 = 28 and,
The Third term = Second term - 8 OR ( 2*a - 8 ) = 28 - 8 = 20
Now consider the third, fourth and the fifth term.
Let, Third term = a = 20
It is evident that Fourth term= 2*a = 2 * 20 = 40 and,
The Fifth term = Second term - 8 OR ( 2*a - 8 ) = 40 - 8 = 32
Similarly consider fifth, sixth and the seventh(term to be found).
Let, Fifth term = a = 32
It is evident that Sixth term = 2*a = 2 * 32 = 64 and,
The Seventh term ( term to calculated) = Second term - 8 OR ( 2*a - 8 ) = 64 - 8 = 56
 

This is an alternating addition and subtraction series. In the first pattern, 10 is subtracted from each number to arrive at the next. In the second, 5 is added to each number to arrive at the next.

2*3 = 6
6*3 = 18
18*3 = 54
54*3 = 162

8 x 1 - 2 = 6
6 x 2 - 3 = 9
9 x 3 - 4 = 23
23 x 4 - 5 = 87
87 x 5 - 6 = 429

The pattern is 
4*2+1=9 
9*2+1=19 
19*2+1=39 
39*2+1=79 
79*2+1=159 
 

The letters decrease by 1; the numbers are multiplied by 2.

This is an alternating division and addition series: First, divide by 2, and then add 8.

This is a simple addition series; each number is 3 more than the previous number.

Let's look at the sequence given:

 70, 71, 76, __, 81, 86, 70, 91, …

A good way to spot a pattern is to try grouping the numbers in “columns” if they seem to repeat every few terms. Notice that if you arrange the terms in groups of three, you get:

 Column 1: 1st, 4th, 7th terms
 Column 2: 2nd, 5th, 8th terms
 Column 3: 3rd, 6th, 9th terms (if there were a 9th term)

Now place the given terms in this layout:

 Column 1: 1st term = 70, 4th term = __, 7th term = 70
 Column 2: 2nd term = 71, 5th term = 81, 8th term = 91
 Column 3: 3rd term = 76, 6th term = 86, (9th term not given)

Notice that in Column 1, the 1st and 7th terms are both 70. It’s natural to expect the missing 4th term in Column 1 to also be 70.

Thus, the blank should be replaced by 70.

The correct answer is (a) 70.

This is a simple alternating addition and subtraction series. The first series begins with 8 and adds 3; the second begins with 43 and subtracts 2.