Let c be the number of cucumbers and t the number of tomatoes.
The total is the sum of the number of cucumbers and that of tomatoes, which is c + t = 280 piece of vegetables
Since there are thrice as many tomatoes as cucumbers, this means c =t/3
Therefore 3*c = t.
The sum will therefore be c + 3*c = 280 pieces of vegetables
This means that 4*c = 280 vegetables
Therefore c = 280/4 = <<280/4=70>>70 cucumbers.
#### 70