First, work out 10% of 12000 as this is a much easier calculation. To do this, one "0" can be taken off the end of the number, to give 1200. Then, to work out 20%, we know that 10x2 = 20. So, 10% of 12000 multiplied by 2 will give us 20%. 10% is 1200.1200 x 2 = 2400 (can do this by calculating 12 x 2 and then adding "00" back onto the end of the answer.