Extend mental methods for whole-number calculations, for example to multiply a two-digit by a one digit, to add and subtract one near-multiple of 1000 from another.
1.add near multiples of 1, 10, 100 and 1000
2.subtract near multiples of 100 and 1000
3.find totals of decimals
4.Informal methods to multiply a two-digit by a one-digit number