I know that this can be done with the iOS iPad (tablet app), and I know that it cannot be done with the Android phone app. I don't know if it can be done with the Android tablet app or the iOS iPhone (phone app). If you are using an iPad, here is how you can do it:

Look in the bottom left corner for an image that's like a squiggly "line" with what looks like a pencil sticking out of its top right corner. Click on this image to bring up what is variously called a sketch pad or scratch pad here. Some things to note:

1. There are 8 different colors plus an eraser tool. There is also an "x" at the top of the color bar to exit this pad. It will always be set to black the first time you use it in a particular problem.

2. In addition to using the "x", you can also exit by pressing the squiggly line image wile in the pad.

3. When you are in the pad, you can still see the question while you are in it, but you can't write your answer until you exit it. So you will have to remember what you wrote or write just the answer on a sheet of paper. One tip - After you have entered your answer but before you click "Check", go back into the pad. You can then compare what you calculated with what you entered, as long as some of your writing doesn't cover the answer box.

4. If you make a mistake, you need to use the eraser tool to remove it. There used to be an undo tool, which was a real time-saver if the mistake was the most recent thing entered, and also got rid of just that last thing, not other things that may be near it.

5. If you need more than that one page in which to do your calculations, tough! Khan Academy got rid of a scrolling feature this page formerly had.

If you are using an Android tablet or an iPhone, you may find the image I just described on your screen. If so, the instructions I gave are the same or similar.

Yeah I’m using it on my iPhone and I don’t have that icon :(