The access code for a cars security system consist of four digits the first digit cannot be 1 and the last digit must be odd how many different codes are avaiable

So we have 10 numbers 0 - 9 
0 1 2 3 4 5 6 7 8 9 
The first digit cannot be 1
therefore there are 9 possibilities 
0 2 3 4 5 6 7 8 9 

digits 2 and 3 can be numbers 0 through 9
therefore there are 10 possibilities for digits 2 and 3 
digits 2 and 3 are a total of 2 digits
and the last digit must be odd so there are 5 possibilities -> 1 3 5 7 9 
so 

 codes available


First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.