Combinatorics + check!

[kathy's]

The Binary system is used to for computer programming. A Binary number consists of a string of digits that are either 0s or 1s
if a string of binary code is 5 digits long, how many binary numbers are possible if the first digit is 1?

1x2x2x2x2 = 16

there are 16 possibilites is this correct? thanks for checking!

 

[pka]

That is correct.
Just think about it.
There are only 32 5-bit strings.
Each begins with a 1 or a 0.
So half begin with 1.