Get your head around addition, subtraction, multiplication and division. Take a visit to Gere's Bike Shop and help them read their graphs and charts. Practise working out the mode, median and mean for a set of numbers. Take a look at time, mass and capacity. Investigate the properties of different shapes. Get your brain ticking with some mental maths questions https://www.bbc.co.uk/bitesize/subjects/z826n39
A daily practise to keep those brain cells sharp http://www.compare4kids.co.uk/maths.php
Practise your tables with the games and activities on this fun site. https://www.topmarks.co.uk/maths-games/7-11-years/multiplication-and-division
Skillswise aims to help adults improve their reading, writing and maths skills. It is targeted at Level 1 of the adult Basic Skills Literacy & Numeracy Curriculums for England, Wales and Northern Ireland.
Woodlands Junior School has several fun online interactive activities to help
not only improve your mental maths skills, but also to help you with SATs
Revision too! https://www.woodlands.kent.sch.uk/page/?title=Mathematics&pid=86