How many three digits codes (single digits 0-9) are possible part A is codes must exceed value of 400 i think answer is 400 multiply 10 multiply 400 or 400x400x400 as three digits

since the code > 400, your choice for the first digit is 6,

you can put 10 different digits in the 2nd spot, and 10 different digits in the 3rd spot

number of possible codes
= 6x10x10 = 600

this would include 400, which cannot be used, since it must be greater than 400
so we have 599 different codes