number of possible cases = 4
number of correct cases = 1
so probability = required/total no of cases
this is equal to 1/4

In Roman numbers, X means 10 and I means 1
XI = 11
IX = 9
when you remove I (i.e. 1)  from both of them, it is X which is remaining i.e. 10.

Total sum of numbers is equal to 4950.
This implies that the sum of numbers in each row should be equal to 990.

group 1 = 1-9 and 90-99
group 2 = 10-19 and 80-89
group 3 = 20-29 and 70 to 79
group 4 = 30-39 and 60-69
group 5 = 40-59

At least one vowel means there may be 1 vowel or 2 vowels or …. 5 vowels
For this question, we consider repetition to be allowed

so, (Total number of cases – cases for no vowel) =cases for at least one vowel

Total number of cases = 26*26*26*26 = 456976
csaes for no vowel = 21*21*21*21= 194481

cases for at least one vowel  are = 456976 – 194481 = 262495