Question

A spy uses maths to form the following sequence of letters. Find the missing letter.

\(\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ A ,\ D ,\ I ,\ P ,\ ?\)

• A. V
• B. Q
• C. Y
• D. S

Answer 1

The correct option is C Y

Numbering the letters in the alphabet, we find:

A	B	C	D	E	F	G	H	I	J	K	L	M
1	2	3	4	5	6	7	8	9	10	11	12	13

N	O	P	Q	R	S	T	U	V	W	X	Y	Z
14	15	16	17	18	19	20	21	22	23	24	25	26

Now, relating the number of each letter to the letters in the sequence, we get:

A	D	I	P	?
1	4	9	16	?

The numbers 1, 4, 9, and 16 are all squares of consecutive natural numbers.
$1^2=1$
$2^2=4$
$3^2=9$
$4^2=16$

Following the rule, we get the next number as:
$5^2=25$

The letter corresponding to 25 is Y.

Hence, the missing letter in the sequence is Y.