# What are the missing letters in this sequence? AI, CL, DP, xx, xx

AI, CL, DP, xx, xx

That's a sequence I found on Quora. The goal is to find what replaces the "x"s. The answer should be letters, not numbers (but you could maybe convert the letters into numbers during the solving process, if that helps).

What letters should replace the "x"s?

AI,CL,DP,GR,KS

Solution:

Convert the letters to numbers 1-9,3-12,4-16,X-X,X-X = A-I,C-L,D-P,x-x,x-x as you can see by adding the value of the letters we get:\begin{align*}9+1&=10\\ 12+3&=15\\16+4&=20,\end{align*}that is, a sequence that increases by five every time: $$10,15,20,25,30$$.
Notice also that the sequence made of first letters has a leapfrog pattern: $$\text{A, C, D}=1,3,4; 1+3=4,$$so the next two initial letters should be $$4+3=7$$ and $$7+4=11$$.
Therefore, our final sequence is $$\boxed{\text{AI, CL, DP, GR, KS}}$$ , where x-x,x-x is $$7-18, 11-19=\text{GR},\text{KS}$$.

• Please hide your answer in spoiler tags (use >! before a line of text) so others can solve this puzzle too, without seeing the answer immediately. Commented Jan 8, 2021 at 17:39
• It doesn't seem like enough evidence for the first digits to be a rot13(yrncsebt frdhrapr) as you claim. Commented Jun 17, 2023 at 22:25

AI, CL, DP, xx, xx

if suppose A is 1 and C is 3 (letter position in english word table)and so on we have

AI : 1 => 9

CL : 3 => 12

DP : 4=>16

from 1=>9 we have (1+9 =10) and 10 is third number that can be devide to 5 (0 5 10) so next number must be 3

also (3 + 12 = 15) so next number is 4

also (4 + 16 = 20) so next number is 5

so we have 5. 5 + ? must generate number that is 25 so number is 20, we can say first "xx" is "ET" (5th english letter) and (20th english letter)

with this sccenario we have: "FX" (6th english letter) and (24th english letter)

5=>20 6=>24

E=>T

F=>X