Here are three clues that students have to find the unknown number to solve the riddle to answer the question. I use Google Forms to have them input their answers. Below is directions on how I create my Google Form. Fun way to practice multiplication and division, especially the third grade standard of Unknown Numbers. I also included a Google Drawing where you can attach the links to your Google Forms (remember to select Preview of the Google Form and that is the link you apply to the Google Drawing).
*To make the forms - Go into your Google Drive and make a New Google Form. Add a title (Lock #1, etc). Then create a short answer question for their name. Next add another short answer question. Lock #1 and #2 I just put Type in the Answer to the Question. Then click on the three little dots on the bottom right corner of the question and click on "response validation". The first drop down should be text, then contains, then the answer (Lock #1 = product, Lock #2 = numerator). Then type in what you want it to say if they get it wrong. In the setting button in the top right corner click on Presentation and type in the message you want your students to get if they are correct. (I put clues for finding the paper for the next lock). If you want your students to be able to try to answer again then make sure to uncheck the "Limit 1 Response" button in settings.