Grid multiplication

In your book, Maths Mela (Chapter 13, The Transport Museum), Amala, Raahi and Farzan visit a transport museum. Raahi spots a toy train. Each coach seats 14 children, and there are 15 coaches. How many children can the toy train seat? We need 15 × 14.

We use a grid. Split 15 into 10 and 5, and 14 into 10 and 4. Then multiply each part by each part: 10 × 10 = 100, 10 × 4 = 40, 5 × 10 = 50 and 5 × 4 = 20. Add all four parts: 100 + 40 + 50 + 20 = 210. So 210 children can sit in the toy train.

The grid works for bigger numbers too. In the aeroplane section, Amala finds a sum: 64 flights, each carrying 152 people. Split 64 into 60 and 4, and 152 into 100, 50 and 2. Now there are six parts: 60 × 100 = 6000, 60 × 50 = 3000, 60 × 2 = 120, 4 × 100 = 400, 4 × 50 = 200 and 4 × 2 = 8. Together, 6000 + 3000 + 120 + 400 + 200 + 8 = 9728 people.

Always check that you have a part for every box of the grid, and add them all. 25 × 34 = 600 + 80 + 150 + 20 = 850, and 68 × 12 = 600 + 120 + 80 + 16 = 816.