A cluster centroid is a finite weighted average. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The centroid numerator is a weighted sum
Position 1 meter has weight 3, and position 2 meters has weight 1.
3×1+1×2=5
Divide by total weight to place the centroid
Total weight is 4, so the centroid is 5 over 4 meters.