whole no.

[shashank.ism]

A positive whole number M less than 100 is represented in base 2 notation, base 3 notation, and base 5 notation. It is found that in all three cases the last digit is 1, while in exactly two out of the three cases the leading digit is 1. Then M equals

a) 31
b) 63
c) 75
d) 91
e) None of these

[Brent@GMATPrepNow]

A positive whole number M less than 100 is represented in base 2 notation, base 3 notation, and base 5 notation. It is found that in all three cases the last digit is 1, while in exactly two out of the three cases the leading digit is 1. Then M equals

a) 31
b) 63
c) 75
d) 91
e) None of these

Nice question, but base 2, 3 and 5 notation is out of scope for the GMAT.
You only need base 10.

[shashank.ism]

Nice question, but base 2, 3 and 5 notation is out of scope for the GMAT.
You only need base 10.

Brent That is a good suggestion. So whether we should try the question with base 2,3,5 etc or leave it...

[ajith]

A positive whole number M less than 100 is represented in base 2 notation, base 3 notation, and base 5 notation. It is found that in all three cases the last digit is 1, while in exactly two out of the three cases the leading digit is 1. Then M equals

a) 31
b) 63
c) 75
d) 91
e) None of these

Which base is 100 highlighted above is in? and to which base is answers are?

On a serious note

31 = 5^2+5+1 ; 3^3+3+1; 2^4+2^3+2^2+2+1

63 =2^5+ 2^4+2^3+2^2+2+1; 2*3^3+3^2; 2*5^2+2*5+3

75 = 3*5^2

91 = 2^6+2^4+2^3+2+1 ; 3^4+2^2+1; 3*5^2+3*5+1

As some of you can see, 91 satisfies all the conditions