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As the lab says, it's okay to use ">" and "<" instead of "≥" and "≤."

The "reporter IF" used here is the simplest and most elegant solution, and you should show it to students when you debrief this lab, but you're more likely to get commands, e.g. this:

Important note: It does NOT work to make a block that takes the average of two numbers and then doThis will tempt students because it follows the pattern of the other exercises so far on this page. But COMBINE can be used only with associative operators, which AVERAGE isn't. The last number to be averaged in will have too much influence. Try these:

The expected, and perfectly correct, solution would beBut DIVISORS OF reports a list of the divisors /in order/, and INTERSECTION doesn't change that, so we already know that the biggest value is at the end of the list.

This solution is a little counterintuitive, because it treats the two lists asymmetrically. We start with LISTA and keep items from it that are also in LISTB. So, expect students to have trouble thinking of this solution.

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KBgAAH6CYJECBAgIAA+wECBAgQIBAICHCAbpIAAQIECByxcQFpoRMBzwAAAABJRU5ErkJggg==2.5 (ITIT): The first KEEP reports the perfect squares less than 100. (In non-squares, divisors come in pairs, e.g., the divisors of 12 include the pairs (1,12), (2,6), and (3,4); each pair multiplies to get 12. In perfect squares, there's a divisor that's paired with itself, e.g., (5,5) for the divisors of 25. And the 5 appears only once in the divisor list, not twice.) The second KEEP reports the primes less than 100. (That comes directly from the definition of "prime": A prime is divisible only by itself and 1.) Make sure kids are impressed by how easy these one-liners are, including the DIVISORS OF block. This is just a glimmer of the power of functional programming; the code would be more complicated and much more bug-prone using a FOR loop.