Re: M25#20

Hi everyone, most fastest way to solve this question is

8_ _, different odd no. will be 8 _ _.
first digit is 8, for odd number third digit will be (1,3,5,7,9) i.e. 5 possibility
2nd digit we can fill from (0-9), since we are looking for different digit so choice for 2nd digit will 10(0-9) - 1st digit-2nd digit with 8 possibility
8 _(8) _(5) = 8*5 = 40


similarly for 9 _ _

for 3rd digit choices are {1,3,5,7}
for 2nd digit choices are 10 - 1st digit-3rd digit = 8

so 8*4=32

so total = 72 different odd digits

Another simple wat to solve is
b/w 800-900 we have 50 odd no.
now we will substract the odd no. like {11,33,55,77,99}= 5
and 881,83,85,87,89 =5
i.e. 50-5-5 =40

b/w 900-999 we have 50 odd no
substract {11,33,55,77,99}=5
and 991,93,95,97,99 = 5
and like 919,929 .....989=8
50-5-5-8 = 32
so different odd number will be 40+32 = 72