Question

Look at this series: $80,10,70,15,60,...$
What number should come next?
A). $20$
B). $25$
C). $30$
D). $50$

Answer 1

We will see the pattern of the series given in the question and then decode the pattern in arithmetic form. Using the arithmetic form, we can find the next number for the given series which is asked in the question.

Complete step-by-step solution:
The given series is: $80,10,70,15,60,...$
Let’s give the position numbers to the numbers in series as: $80 - 1,10 - 2,70 - 3,15 - 4,60 - 5,...$
We can see a drastic change in numbers of every even and odd position.
So, let’s consider the odd position starting from $1$ and even position starting from $2$,
The odd position series is $80,70,60,...$
The even position series is $10,15,...$
We are asked to find the next number after $60$ and we know the number which will come after $60$will take an even position as the number $60$ is at an odd position.
The pattern for the even series is: starting number is $10$ and the next number is $15$ .
So, we can conclude that, in even series starting from $10$, every number is added with $5$ by the previous number.
The next number after $15$ in the even series will be added with $5$ by the previous number i.e., $15$ .
$15 + 5 = 20$
Therefore, the next number after $60$ in the given series which will take the even position will be $15 + 5 = 20$.
The correct option is option A. $20$.

Note: A series of numbers is the operation of adding infinitely many quantities, one after the other, to a given starting quantity. In the above example, the starting number is $80$ and the series is formed by adding a certain number to the starting number and so on.