The pair of numbers smaller than 10 with first common multiple greater than 50 are (7, 8), (8, 9) and (7, 9).
For (7, 8):
If 7, 14, 21, 28, 35, …, 49, 56, 63, … are said ‘idli’.
And 8, 16, 24, 32, …, 48, 56, 64, … are said ‘vada’.
Then 56 is the first number (first common multiple of 7 and 8) greater than 50 which would be said ‘idli-vada’.
For (8, 9):
If 8, 16, 24, 32, …, 48, 56, 64, 72, … are said ‘idli’.
And 9, 18, 27, 36, …, 54, 63, 72, … are said ‘vada’.
Then 72 is the first number (first common multiple of 8 and 9) greater than 50 which would be said ‘idli-vada’.
For (7, 9):
If 7, 14, 21, 28, …, 49, 56, 63, 70, … are said ‘idli’.
And 9, 18, 27, 36, …, 54, 63, 72, … are said ‘vada’.
Then 63 is the first number (first common multiple of 7 and 9) greater than 50 which would be said ‘idli-vada’.