Problem: if you write down all the numbers from 1 to 100 , then how many times do you write 3 ?
Rationale: "explanation : explanation : clearly , from 1 to 100 , there are ten numbers with 3 as the unit ' s digit - 3 , 13 , 23 , 33 , 43 , 53 , 63 , 73 , 83 , 93 ; and ten numbers with 3 as the ten ' s digit - 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 . so , required number = 10 + 10 = 20 . answer : c"
annotated_formula: divide(subtract(100, 1), 3)