how many integers between 2000 and 3000 that have distinct digits and increase from left to right ?
since the numbers must be distinct and increasing from left to right , the only arrangements we could come - up with are : 245 _ - - > 4 246 _ - - > 3 247 _ - - > 2 248 _ - - > 1 256 _ - - > 3 257 _ - - > 2 258 _ - - > 1 267 _ - - > 2 268 _ - - > 1 number of integers = 20 b
divide(factorial(multiply(divide(2000, const_1000), divide(3000, const_1000))), multiply(factorial(divide(3000, const_1000)), factorial(divide(3000, const_1000))))