math
posted by arzam on .
a two figure number is written down at random find the probability
a)that the number is greater than 68
b)the number is a multiple of 9
c) it is less than 100
d) it contains at least one 5 (i.e a number such as 15 or 55

There are 90 2digit numbers
a) 32 are greater than 68, so prob = 32/90
b) 10 are multiples of 9, so ...
c) all are less than 100, so ...
d) 18 have at least one 5, so ... 
There are 90 twodigit numbers (1099).
a) 31/90 = ?
b) 18, 27, 36, 45, 54, 63, 72, 81, 90, 99 are multiples of 9.
c) All twodigit numbers are less than 100.
d) 15, 25, 35, 45, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 65, 75, 85, 95 all have at least one 5. 
My bad on (a). PsyDAG is correct

thanks PsyDAG and Steve