How to solve Tetrach puzzles;

Add all the numbers in the circles, subtract the number

of stones and divide by two. This will give the number

of pebbles that go in the centre triangle. Then all the

other triangles can be found by subtraction.

Why this works;

Let the number of pebbles in the

triangles be a, b, c and d

Then a + b = 62

c + b = 48

d + b = 54

Adding these three equations gives

a + 3b + c + d = 164

But we know that the total number of stones is 100 so

a + b + c + d = 100 and if we subtract this we get

2b = 64

so b = 32 and from our original equations we can find a = 30, c = 16, d = 22