Grandpa's taking all the grandkids to the neatest amusement park ever: Safari Park. All the Jungle King rides cost 4 tickets. Rhino Rodes are just two tickets. Monkey Games and Tiger Treats are a bargain at one ticket each. But how will the kids spend their tickets if they want to ride the "spectacular, amazing, heart-pounding Terrible Tarantula" which costs 6 tickets?!
An essential part of early algebraic thinking is understanding a "number sentence" with missing elements (8+?=20), and the process for figuring out the unknown.