Logical Reasoning - Number Series - Discussion

In each series, look for the degree and direction of change between the numbers. In other words, do the numbers increase or decrease, and by how much

2. 

Look at this series: 7, 10, 8, 11, 9, 12, ... What number should come next?

[A]. 7
[B]. 10
[C]. 12
[D]. 13

Answer: Option B

Explanation:

This is a simple alternating addition and subtraction series. In the first pattern, 3 is added; in the second, 2 is subtracted.

Praveen said: (Sep 23, 2010)  
Add 1 to the odd positioned (7, 8, 9, 10) numbers, and add 1 to the even positioned numbers (10, 11, 12).

Bharat said: (May 6, 2011)  
One more thing every alternate number increase as 7, 8, 9, 10.

Rahul said: (Jul 2, 2011)  
I want a solution of this one

Kasi said: (Aug 19, 2011)  
I want more explanation about this with more examples example.

Harikrishnan said: (Aug 24, 2011)  
It has the alternating series as 7, 8, 9 and 10, 11, 12. So the next series will be 10, 13. Like that.

Somu.K said: (Aug 29, 2011)  
7+3=10
10-2=8
8+3=11
11-2=9
9+3=12
12-2=10

So, Answer is 10.

This is correct or not?

Jabin said: (Sep 22, 2011)  
Correct.

Rohit.Rcert said: (Sep 26, 2011)  
It's obivously a alternate series of number in which numbers are changed by +3 and then -2 in A order.
and as praveen suggest A idea of breaking this chain into two sub chain of number....1st odd place number then 2nd even place number ant then each number of series is changed by +1 is a very nice shortcut...appriciate.

Juhi said: (Sep 28, 2011)  
Thanks Somu.K great explain. Thanks. Friend.

Gaurav said: (Nov 13, 2011)  
Somu is right

Balvir said: (Jan 4, 2012)  
7+3=10-2=8+3=11-2=9+3=12-2=10 Ans

Shanthi said: (Mar 8, 2012)  
7+3=10-2=8+3=11-2=9+3=12-2=10

Sharanya said: (Jun 27, 2012)  
This answer is simple.

1st add 3, next subtract 2.

7+3=10.

10-2=8.

8+3=11.

11-2=9.

9+3=12.

12-2=10.

Answer 10.

Bhushan Salunkhe said: (Sep 8, 2013)  
7+3=10
10-2=8
8+3=11
11-2=9
9+3=12
12-2=10

Because look the series of addition and subtraction 1st add 3 you get 10 then subtraction 2 you get 8 same next again add 3 get 11.

Again same - 2 get 9 again add 3 get 12 obviously next is subtraction 12-2 = 10.

The series + - + - + -

Debendra said: (Sep 26, 2013)  
7+3=10
8+3=11
9+3=12
10+3=13
Answer 10

Ishwar.Kesari said: (Dec 17, 2013)  
In first number adding three and second number subtracting two and so on you will get the missing number.

Anusha said: (Jan 23, 2014)  
7, 8, 9, 10...

10, 11, 12...

Then we place 7, 10, 8, 11, 9, 12, 10.

Debendra said: (Feb 19, 2014)  
Look at this series: 7, 10, 8, 11, 9, 12, .

Ans -7+3 = 10,
8+3 = 11,
9+3 = 12,
10 -- Ans (7+1,8+1, (9+1) - Ans.

Pavan Bhushan said: (Apr 21, 2014)  
This is an alternating series.

1st series is 7, 8, 9, 10,.....
2nd series is 10, 11, 12, 13,.....

Zuqarnain said: (Jun 6, 2014)  
there are actually two series,

7, 8, 9, 10...

10, 11, 12...

So,

we place 7, 10, 8, 11, 9, 12, 10.

Saral Killer said: (Jul 6, 2014)  
7, 10, 8, 11, 9, 12, ?

The answer is 10 why because.

Just those are compare to above series in that 7, 8, 9 and 10, 11, 12 sequence no's are display so after 7 comes 8 and after 8 comes 9 and after 9 comes 10 so answer is "10".

Veeradevi said: (Jul 22, 2014)  
Suggest me if the logic is wrong.

Add sequence of 3,4,5... in the odd position to the 7 and add sequence of 1,2,3.... in the even position to the 7 then we get our required result.

7+3 = 10.
7+1 = 8.
7+4 = 11.
7+2 = 9.
7+5 = 12.
7+3 = 10.

Sadichha said: (Oct 11, 2014)  
This is a simple alternating addition & subtraction series.

7+3=10. 8+3=11.
10-2=8. 11-2=9.
9+3=12. 12-2=10.

Katroth Ram said: (Nov 7, 2014)  
Answer is : 10.

Solution is: 7+3 = 10, 10-2 = 8, 8+3 = 11, 11-2 = 9, 9+3 = 12, 12-2 = 10 is correct or not.

Durga said: (Nov 24, 2014)  
How do we take first 3 only? Please answer the question because I would like to learn the reasoning ability.

Devi said: (Dec 8, 2014)  
Why should we take the number 3?

Jai Kishan said: (Jan 6, 2015)  
Can any one explain it briefly with more examples?

Shrikant said: (Jan 17, 2015)  
Add all the numbers and then divide it with 6. Because there are total 6 nos given, as the answer will come.

E.g: 7+10+8+11+9+12=57.

57/6 = 9.5.

Round figure is 10.

Shubhi said: (Jan 23, 2015)  
Here a simple concept is taken under use that is take first no 7.

Follow logic that once you add 3 in that no so:

7+3 = 10.

That whatever no you get now subtract by 2.

10-2 = 8. (continues process).

So again add 3 whatever got subtract by 2 and continues series.

Shiva Kumar Singh said: (Mar 22, 2015)  
7 add 3 equal 10.
10 subtract 2 equal 8.
8 add 3 equal 11.
11 subtract 2 equal 9.
9 add 3 equal 12.
12 subtract 2 equal 10.

So that answer is 10 right.

Macanet said: (May 3, 2015)  
What makes 10, the answer?

Perin said: (Aug 2, 2015)  
Answer should be 10. Add 1 to alternate numbers.

Chandu said: (Aug 10, 2015)  
Answer is 10.

7+3 = 10-2 = 8+3 = 11-2 = 9+3 = 12-2 = 10.

Uday said: (Sep 23, 2015)  
First find out the difference of these nos

7-10=3.
10-8=2.
8-11=3.
11-9=2.
9-12=3.

Consider no 3 as no 2 as now.

7+3=10.
10-2=8.
8+3=11.
11-2=9.
9+3=12.
12-2=10.

Tulasi said: (Sep 26, 2015)  
Odd positions are increased by 1. And even positions are increased by 1.

Rohan Kumbhar said: (Feb 28, 2016)  
Very simple. First 3 is increased and second 2 is decrease.

Santosh said: (Apr 7, 2016)  
Answer is 10.

Deepshikha said: (Jun 28, 2016)  
Its simple 3 add in first-time subt. 2 in second time.

7 + 3 = 10,

10 - 2 = 8,

8 + 3 = 11,

11 - 2 = 9,

Then,

12 - 2 = 10.

Divya said: (Jul 20, 2016)  
Thank you so much for giving a various explanation.

Mohd Moin Ansari said: (Aug 2, 2016)  
As per the logic, 12 - 2 = 10.

Aditya Vamsi said: (Aug 24, 2016)  
Just we have to use the jumbling system among the number in ascending order.

M.Raghram Pgdm 1 said: (Aug 24, 2016)  
The logic is, Take difference 3 and add 2 alternatively.

John Taniang said: (Aug 25, 2016)  
Two series 7, 8, 9 and 10, 11, 12.

So 10 is the answer for the first series.

Vinay said: (Sep 12, 2016)  
Thank you so much for giving a solution with various explanation.

Krishnarathod said: (Sep 21, 2016)  
7, 8, 9, and next 10.
10, 11, 12 next is 13.

So, the answer 10 is correct.

Ayush Kumar said: (Sep 25, 2016)  
If we see the series, we can see that alternate digits are incorrect sequence 5.

7, 8, 9 then 10.

10, 11, 12.

Simmi said: (Oct 6, 2016)  
7 + 1 = 8,
10 + 1 = 11,
8 + 1 = 9,
11 + 1 = 12,
9 + 1 = 10. Add 1 alternatively.

Sedhumadhavan said: (Oct 14, 2016)  
First we find difference between each two numbers.

Then that comes,

7, 10 - 2 numbers is difference.
10, 8 - (-1) number is difference.
8, 11 - 2 number is difference.
11, 9 - (-1) number is difference.
9, 12 - 2 number is difference.

Next number is see before the series is 2, -1, 2, -1, 2.

Then finally we consider difference is -1. So, the answer is 10.

Navadurga said: (Oct 19, 2016)  
Here,
7 + 3 = 10,
10 - 2 = 8,
8 + 3 = 11,
11 - 2 = 9,
9 + 3 = 12,
12 - 2 = 10 according to this B is correct answer.

Srimathi said: (Oct 20, 2016)  
It's a very simple.

7, 10, 8, 11, 9, 12, ...
Divide in to two parts.

1st -> 7 8 9.
2nd -> 10 11 12.

So the next number would be 10.

Jagabandhu Jena said: (Dec 29, 2016)  
Yes, 10 is right answer.

Jada Dalei said: (Feb 1, 2017)  
Nice solution, Thank you all.

Kaderkhan said: (Mar 5, 2017)  
Please solve this 11, 22, 55, 165, ....

a. 495.5
b. 325.5
c. 577.5
d. 333.5

Chetan said: (Mar 28, 2017)  
2, 3, 7, 17, 31, 53,.....

Find the next number please.

Ajit Singh said: (Jul 25, 2017)  
1th line : 7.8.9.
2th line 10.11.12.

Ans : 10.

Sumeet Kumar said: (Aug 29, 2017)  
Thanks for sharing good efforts.

Rajni Gangwar said: (Oct 15, 2017)  
18, 1, 14, 9, ?, 12, 21.

What number should place at question mark?

Madhavi said: (Jan 22, 2018)  
Nice explanation. Thanks.

Seema Roy said: (May 21, 2018)  
How will we understand which numbers to be subtracted & added?

Please explain.

Srisai.Putta said: (Sep 4, 2018)  
Just add & subtract the digits given in series 7, 10, 8, 11, 9, 12.

Ans:7+3=10, 10-2=8, 8+3=11, 11-2=9, 9+3=12, 12-2=10 :. Next coming number in the given series is 10.

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