Tom had 10 x 5 = <<10*5=50>>50 miniature racing cars.
Tom gave 50 x 1/5 = <<50*1/5=10>>10 miniature racing cars to each of his two nephews.
So, he gave a total of 10 x 2 = <<10*2=20>>20 cars to his two nephews.
Therefore, Tom is left with 50 - 20 = <<50-20=30>>30 miniature racing cars.
#### 30