Answer:
The answer to your question is There were 59/168 muffins left.
Step-by-step explanation:
Data
Initial amount of muffins = 1
Amount of muffins given to his neighbors = 11/21
Amount of muffins eaten = 1/8
Amount of muffins left = ?
Process
1.- Subtract the amount of muffins given to the neighbors and the amount of muffins eaten to the initial amount of muffins.
       1 - 11/21 - 1/8 =
-Look for the greatest common factor
          21  8   2
          21  4   2
          21  2   2
          21   1   3
           7     7
           1
  GCF = 2 x 2 x 2 x 3 x 7
      = 168
-Solve the arithmetical operation
       1 - 11/21 - 1/8 = (168 - 88 - 21) / 168
                  = 59/168
-Conclusion
There were 59/168 muffins left.
