Solution

195901

Problem / game
Domino sets Back to problem
First name
Isaac, Felix, Alba, Hugo
School
Park Hill Junior School
School's Twitter handle
@ParkHillJunior 1
Country
United Kingdom, UK
Age
8

There should be 8 of each number so you count 8 sixes, 8 fives, 8 fours, 8 threes, 8 twos, 8 ones and 8 blanks.
The key to finding the missing ones is:
Line them up in rows or columns of its number.
OR:
There should be 28 dominoes in a pack so you count them.
4x7=28