About this exercise
Number sense — magnitude estimation without exact calculation — is a foundational math skill that develops in childhood.
You see a problem (e.g., 73 × 47) and pick which of two answers is closer to truth. The wrong answer is in the right ballpark, so guessing fails.
Skilled estimators round and re-anchor (73 × 47 ≈ 70 × 50 = 3500).
Strongly correlated with later math achievement and STEM career success.