how many 4 digit even numbers do not use any digit more than once
"a b c d ( thousand , hundreds , tens , units ) d can be 0 2 4 6 8 ( any of the 5 digits ) a can be anything except ( d or 0 ) so 8 possibilities c can be anything except a and b so 8 possibilities b can be anything except ( a d c ) so 7 possibilities total ways are 8 * 7 * 8 * 5 = 2240 ans : c"
add(subtract(subtract(const_1000, const_10), multiply(multiply(const_10, multiply(4, 4)), multiply(const_4, const_2))), const_10)