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We really enjoyed this challenge! We found that to begin with we didn't understand what we were dealing with - we didn't really know how dominoes worked.
We looked at the full set of dominoes and quickly discovered that there were 28 dominoes - which means that Amy has lost 4.
We then started looking at the numbers of spots on the dominoes and discovered that there is only ONE of each type (so there will be only ONE tile with a two and a three on it for example).
When we arranged them in order of total spots, we noticed a pleasing pattern. which you can see in the photo that we have attached. We noticed that some totals (0,1,11 and 12) only occurred once. 6 was the most likely total to find as there were four tiles with this.
By arranging the tiles like this, we found that we could use our tables to help us find the total of all the spots... We added 1x1 to 2x2 to 2x3 to 3x4 to 3x5 to 4x6 etc.
Our total was 168.
We now knew that Amy was missing FOUR dominoes and that she was missing 43 spots.
So, which four was she missing?
The Smarty Plants quickly worked out that there was one way to make 43 with four dominoes - the two 10s, the 11 and the 12.
Some of our group though (who hadn't set their dominoes out in order) wasted a bit of time looking for other ways to do it... The ones that understood the possibilities didn't!
An extension question...
Amy's friend Bert also has a set of dominoes. He too has lost some.
He only has 18 dominoes and only a total of 114 spots! Which dominoes has Bert lost?