Doubling and halving

Open your book, Maths Mela (Chapter 9), at page 133 and read the poem 'The Doubling Magic'. In the poem, Magician Anvi visits Gulabo's house. She pulls 23 flowers out of her coat, and with her magic the flowers double. Doubling means making twice as many: 23 + 23 = 46. Now there are 46 flowers.

Your book has a table of flowers before and after the magic, and the magic always doubles. 10 flowers become 20. 45 become 90. 150 become 300. To double a bigger number, double each part: double of 45 is double of 40 (80) and double of 5 (10), so 90.

Halving undoes doubling. If there are 222 flowers after the magic, there were half of 222 before: 111. 410 came from 205, and 500 came from 250.

Look at the ones digit of a double. Double of 28 is 56, which ends in 6. Double of 45 is 90, which ends in 0. Double of 17 is 34, which ends in 4. A double always ends in 0, 2, 4, 6 or 8, so a double is always an even number. It can never end in 1, 3, 5, 7 or 9.