Two new sets of pages, using bar models, have just been published in our Year 4 Addition category. They are both hard to do mentally and may need the help of jottings. For example, in the first set, a question such as: 623 + 127 could be done mentally, with jottings, or using the formal written method. When it comes to mental addition I usually do it in the reverse order than on paper, adding the hundreds, then the tens and finally the ones. I add 600 and 100 to make 700, then 20 and 20 to make 740 before finishing with the 3 and 7 to make a further 10, making a final total of 750. When doing these think of the approach that you use, which may well be different from the above.
The second set has word problems using 4-digit numbers, which are really stretching the limits of mental arithmetic and children should decide whether they need to write the sum out to find the answer.
We also have published questions of a similar style in our Year 4 Subtraction category, again using bar models and allowing children to decide the best approach to working out the answers. It is always a good idea to ask children why they chose a particular approach.