Posted by arzam on Thursday, May 2, 2013 at 1:40pm.
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

math  Steve, Thursday, May 2, 2013 at 2:09pm
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 ... 
math  PsyDAG, Thursday, May 2, 2013 at 2:15pm
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. 
math  Steve, Thursday, May 2, 2013 at 2:19pm
My bad on (a). PsyDAG is correct

math  arzam, Thursday, May 2, 2013 at 2:42pm
thanks PsyDAG and Steve