Marcel bought 10 ears of corn and Dale bought 1/2 what Marcel did, 10 x 1/2 = 10/2 = <<10*1/2=5>>5 ears of corn that Dale bought.
Together, Marcel and Dale bought 10 + 5 = <<10+5=15>>15 ears of corn, or 15 vegetables.
They end up buying 27 vegetables total, and from those 27, 15 of them were corn.
The rest of the vegetables are potatoes, 27 vegetables - 15 ears of corn = <<27-15=12>>12 potatoes.
Dale bought 8 potatoes, so Marcel bought 12 - 8 = <<12-8=4>>4 potatoes.
#### 4