Concept:The seller used repeated addition (₹6 + ₹6 + ₹6 + ₹3) to charge ₹21 for 350 g of spinach. This is an informal mental math strategy, not a standard calculation.
Explanation:Actual cost of 350 g at ₹60/kg = 350 g × ₹0.06/g = ₹21.
The seller avoided using a weighing scale and instead split 350 g into four parts: three parts of about 93.75 g each (charged ₹6 each) and one part of about 68.75 g (charged ₹3).
This method is not ambiguous (A is false) because it clearly works for this transaction.
It is useful for mental math in daily life, so it is not useless for solving problems in class (B is false).
Such alternate strategies help students think flexibly and develop new problem‑solving approaches (C is true).
Answer:Only C → Option D.