A two-step money puzzle

Open your book, Maths Mela, at page 99 and read the poem 'A Strange Puzzle!'. It is a maths puzzle told as a rhyme.

In the poem, four children, Krishna, Sudama, Mala and Neela, go for a walk and find a farmer with fresh oranges. One orange costs ₹21. Each child buys two oranges. Then each child pays with a different note: Krishna with ₹50, Sudama with ₹100, Mala with ₹200 and Neela with ₹500. The poem asks: what balance does each child get?

This puzzle has two steps. Step 1: find what each child has to pay. Two oranges cost ₹21 + ₹21 = ₹42. Every child pays the same cost, ₹42.

Step 2: find each balance. Balance = money paid − cost. Krishna gets ₹50 − ₹42 = ₹8. Sudama gets ₹100 − ₹42 = ₹58. Mala gets ₹200 − ₹42 = ₹158. Neela gets ₹500 − ₹42 = ₹458. The cost is the same, so the bigger the note, the bigger the balance.