Even # --------- if it ends with 0, # of ways = 6*5*4 = 120 if not, 3 ways for ending digit, 5 ways for 1st digit, 5*4 for middle digits = 300 so total ways = 420 odd # --------- 4 ways of ending digit, 5 ways for 1st digit, 5*4 for middle digits = 400 ways < 4000: ---------- 3 ways for starting digit, 6*5*4 ways for remaining digits = 360 ways > 3000 & < 4000 ------------------------ 1 way for starting digit , 6*5*4 for remaining digits = 120 ways