# Logical Reasoning - Number Series - Discussion

### Discussion :: Number Series - Type 2 (Q.No.2)

Look carefully for the pattern, and then choose which pair of numbers comes next.

2.

8 11 21 15 18 21 22

 [A]. 25 18 [B]. 25 21 [C]. 25 29 [D]. 24 21 [E]. 22 26

Explanation:

This is an alternating addition series, with a random number, 21, interpolated as every third number. The addition series alternates between adding 3 and adding 4. The number 21 appears after each number arrived at by adding 3.

 Deepanshu said: (Nov 24, 2010) I do not seem to get this one. Please explain in layman

 Monica said: (Nov 27, 2010) Can you explain the addition series in detail? please.

 Durai said: (Dec 16, 2010) This is simply confusing. I think, this question is wrong.

 Manas said: (Jan 13, 2011) Kindly explain it elaborately, I could not understand the solution.

 Saurabh said: (Jan 16, 2011) Hi, Random number is 21 and is repeated after two number. 3 is adding to 22 the result is 25 and 21 is repeated again.

 Sankari said: (Feb 11, 2011) 8+3 = 11 11+4 = 15 15+3 = 18 18+4 = 22 From above we can conclude as difference b/w first two no.is 3. Third no. is interpolation, it is repeated as every third no. so next pair is 25 21 (22+3 =25)

 Sriharsha said: (Feb 15, 2011) What is interpolation?

 G.Priyanga said: (Feb 17, 2011) I did not get this answer. Please explain it clearly.

 Prathyusha said: (Feb 22, 2011) 11-8=3 15-18=3 22-25=3 so 25 21 is answer

 Sameh said: (Mar 3, 2011) I'm not convinced , if the answer was only 25 it would be ok but 25 21 is confusing..

 Siva said: (Mar 5, 2011) What is your confusion boss it is easy to get because hare to first number first 3 is added and then as third number interpolation would come and then what is there before interpolation number that would be added by 4 like this it will be go on.

 Sundar said: (Mar 22, 2011) 8 11  15 18  22 25  29 32  36 39  43 46  .... Here 3, 4 is added alternatively and  injected as given below: Inital = 8 8 + 3 = 11 **********  11 + 4 = 15 15 + 3 = 18 **********  18 + 4 = 22 22 + 3 = 25 <----- Required Answer **********  <----- Required Answer 25 + 4 = 29 29 + 3 = 32 .........etc

 Priya said: (Mar 31, 2011) Among all the above solution, I think Sundar is right.

 Azhar said: (Apr 3, 2011) Good explained by Sundar.

 Bharat said: (May 9, 2011) Thanks Sundar.

 Vipin said: (Jun 10, 2011) Great job sundar.

 Navjot said: (Jul 9, 2011) 8,11,,15,18,,22,25,,29,32, 1st no is 8,when 7 is added ,it gives 15 (4th number in series) 2nd no is 11 ,again when 7 is added,it gives 18(5th no in series) 21 is interpolated as every 3rd no. 4th no is 15 ,when 7 is added,it gives 22 (7th no) 5th no is 18,when 7 is added,it gives 25 (8th no) again 21 is interpolated as 3rd no (here its 6th). 7th no is 22 ,when 7 is added,it gives 29 (10th no) 8th no is 25,when 7 is added,it gives 32 (11th no) again 21 is interpolated as 3rd no (here its 9th).and so on.....

 Shankari said: (Sep 12, 2011) Really great, I can understand sundar's explanation thank you.

 Sudhakar said: (Nov 12, 2011) Actually it would be 25, 29. Adding 3 and alternate adding 4. So it should come 25, 29.

 Simarpreet Kaur said: (Nov 18, 2011) I am not able to understand it please explain it as a layman could understand.

 Priyanka said: (Nov 21, 2011) SOLUTION: Here number 21 put as a interpolatn dat means only to confuse you. So just excluding that series will be like as: 8+3=11 (add 3 & interpolation 21) 15+3=18 (add 3 & interpolation 21) Now 22+3 =25 (add 3 & interpolation 21) So answer wil be B) 25 21 because 25 final anwer and 21 as a interpolation. Hope now you get it.

 Saikanth said: (Mar 4, 2012) 8+3 = 11 11+4 = 15 15+3 = 18 18+4 = 22 From above we can conclude as difference b/w first two no.is 3. Third no. is interpolation, it is repeated as every third no. so next pair is 25 21 (22+3 =25)

 Paramjeetkaur said: (Mar 10, 2012) Thanks Sundar.

 Saravanan.O said: (May 25, 2012) There are two condition is here 1. Every 3rd number is 21 2. Difference between 2 and 1 number is 3. In this way, 8-11=3 21 15-18=3 21 22-25=3. so the answer is 25 21

 Harpreet Singh said: (Oct 21, 2013) 21 is common after every 2 number. So 8 11 21 15 18 21 22... 8+3 = 11 21. 15+3 = 18 21. 22+3 = 25 21. So answer is 25 21.

 Ashish Minz said: (Mar 7, 2014) @Harpreet Singh. How he get 3.. 11-8 = 3 21 is fixed. 18-15 = 3.

 Hasan Faraz said: (Apr 24, 2014) Good question. 8 11 21 15 18 21 22 It is a sequence of adding 3, putting 21, adding 4 to the result of adding 3.

 Ashok Bijoy said: (May 5, 2014) 8(+3) = 11, 21. 15(+3 = 18, 21. 22(+3) = 25, 21.

 Dharmishtha said: (Jul 1, 2014) (8+3)=11 & 21 is common in this series. (15+3)=18 & 21 is common in this series. (22+3)=25 & 21 is common in this series. So, 8, 11, (21), 15, 18, (21), 22, 25, (21),...

 Jeyanthi said: (Oct 9, 2014) This type of question is easy but clearly understand the logic.

 Ganesh said: (Nov 10, 2014) 8+3 = 11 15+3 = 18 22+3 = 25 So 21 is common in this series.

 Zakariya said: (Jun 10, 2015) I don't understand this type questions.

 G.N.Lakshmi said: (Jan 16, 2016) 8+3 = 11. 15+3 = 18. 22+3 = 25. 21 is median.

 K Devraju said: (Mar 14, 2016) 21 is Common in this Series. So you can See, => 8 + 3 = 11. => 15 + 3 = 18. => 22 + 3 = 25. Answer comes (25 21).

 Kapil Kapoor said: (Jun 15, 2016) @Sundar, Thanks for the wonderful explanation.

 Subhash said: (Jun 27, 2016) @ Sundar Thank you, your explanation is very good.

 Shridhar said: (Aug 20, 2016) @Sundar, good answer but please tell me in a simple way.

 Rama Kant said: (Sep 26, 2016) 8 + 7 = 15, 15 + 7 = 22, 11 + 7 = 18, 18 + 7 = 25, 21 is constant. Every number add 7 except 21.

 K.Chandra Babu said: (Oct 28, 2016) Leaving 21 as a third number. 8 + 3 = 11, 15 + 3 = 18, 22 + 3 = 25 so answer will be 25 21, and also first number difference is 7.

 Divakar .U said: (Nov 21, 2016) 8 11 {21} = The difference is 3. 15 18 {21} = The difference is 3. 22 25 {21} = The difference is 3.

 Swapneswar said: (Jan 6, 2017) Good explanation @Sundar.

 Maranna T said: (Mar 25, 2017) Thanks for all the given explanation friends.

 Salman Khan said: (Apr 19, 2017) 8 11 21 15 18 21 22 25 21 8 + 3 = 11 21 15 + 3 = 18 21 22 + 3 = 25 22.

 Mehtab said: (May 1, 2017) There is a mistake in explanation. 21 is repeating as random number while 7 is added to each pair to get the new pair.

 Annam Kanaka Nishanth said: (Sep 6, 2017) 11.21-8=3.21 15-11.21=4.21 18.21-15=3.21 22-18.21=4.21 Hence 22+3.21=25 21.

 Soham Shinde said: (Sep 8, 2017) Nice explanation @Saurabh.

 Pradip Paul said: (Feb 18, 2018) 8+3=1121. 15+3=1821. 22+3=2521. Ans is 2521 (B).

 Priya Kumari said: (May 8, 2019) Hi, I am not understanding this, Please anyone help me.

 Prajwal said: (Jul 2, 2019) Thanks for all for explaining it.

 Dinesh said: (Jul 4, 2019) Thanks for explaining the answer @Sundar.

 Srikanth Singh said: (Aug 2, 2019) Thanks @Sundar.

 Sarveshwar said: (Aug 20, 2019) 8+3=11, 11-21=10 10+3=13. 15-18=3, 18-21=3 3+3=6. Then 13-6=7. 22+3=25, 25-4 = 21. 22,25,21.

 Sushil said: (Apr 18, 2020) 25 29 is the correct answer.

 Anshu said: (Feb 11, 2021) @Sundar and @Navjot. Good explanation, Thanks.

 Fama said: (Aug 13, 2021) 2529 is the correct answer.