fameatop-See my comments below in red...

debayan222 wrote:

1. A code signal uses digit-letter-digit combinations but 0 and 1 are not used for either digits or letters.How many code signals are possible ?

(A) 1536

(B) 1456

(C) 1024

(D) 1628

(E) 856

Bunuel- can you please explain in detail ?

Places need to be filled (or the number of ways to form a 3 digit number if Digits or letters can be repeated) = D L D

Only 8 digits can be used to make a signal as 2 digits (0 & 1) are not allowed

Letters that can be used to make a signal = 26

Letter or digits can be used repeatedly as we have to form a code (3A3 is different from 3A1)

First place can be filled in = 8 ways

2nd place can be filled in = 26 ways

3rd place can be filled in = 8 ways

Total no of ways to form a code = 8 x 2

6 x 8 = 1664

Yup..!if you're to consider repetition then it's the answer...but it doesn't say that explicitly..I really doubt the language of this question. If the above options are correct, then question must state explicitly that DIGITS can be used only ONCE. In this case, answer will be 8 x 26 x 7=1456

You've very rightly said that the question is indeed ambiguous...Even I've had the this answer..Hope it helps.