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 28 x 8 = 1664
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 that case, answer would be 8 x 26 x 7=1456
Hope it helps.
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