A friend from China gave us a bag of walnuts plucked from their home-grown walnut tree. I decide to count them by applying math:
A stack of walnuts piled in a pyramid, with base layer arranged in a square of 6×6 walnuts, above layers 5×5, 4×4, 3×3, 2×2, and finally top 1 (1×1).
How many walnuts are there in total ? (Answer: 91)
This is simple math but only taught in A-level (with proof by induction).
Hint: Watch free Khan Academy Math lecture to learn more ….
Below is a 400-year-old walnut tree: walnut is called “Wise fruit 聪明果”, it looks like human brain, also has proven nutritious benefits to brain.