When working with large numbers it is not possible to answer lots of questions within one minute, but it is surprising just how many correct answers can be achieved with top-notch mental arithmetic skills. Four new games for Year 5 have just been published:• Subtract from 1,000• Subtract from 10,000• Subtract a multiple of 10,000• Subtraction around the thousands boundary.The first time questions such as these are met it can take quite a few seconds to work out the best method for finding answers quickly and correctly. For example:1,000 – 270can be done by adding 30 to 70 to make 100 and then adding 700 to make 1,000.However, perhaps even quicker is a nifty technique of making the hundreds digits add up to 9 and then the tens digits add up to 10; 7 in the hundreds, 3 in the tens and zero in the ones.This can be developed further with a question such as:10,000 – 3,456• Make the thousands digits add up to 9: 6• Make the hundreds digits add up to 9: 5• Make the tens digits add up to 9: 4• Make the ones add up to 10: 4• Answer: 6,544.We will return to this idea later with some even harder subtraction. Meanwhile have a go at both our Year 5 and Year 6 subtraction one minute challenges and see if a gold certificate can be achieved.Year 5 Subtraction On-screenYear 6 Subtraction On-screen