This mental math interactive worksheet is for students who have started to learn about numbers up to 100. It consists of three sets of tasks, each task containing 15 examples.

In the first set, students have to add 1, in the second set they have to subtract 1 and in the third set there are mixed problems.

Hidden in the background of the tasks is a picture on the theme of space. Students discover it piece by piece by writing down the correct answers about addition and subtraction up to 100.

It is very easy for the teacher to check how well the students are doing. It only needs to look at how much of the image they have already managed to show.