Need a bit of help with your mental addition and subtraction? Take a look at this link for some ideas. Remember how important it is to use your place value. Also, if you are finding it hard to keep the numbers in your head try using your fingers to represent or count. You can also draw out your hundreds, tens and ones representations. Most importantly, try practising counting up and down over 10's and 100's as this is really good practise so that you know what comes before and after a multiple of 100.