These free printable worksheets give the first three terms of a sequence and ask for the sum of the first n. Every sum is a whole number, and the answer key shows where the formula comes from rather than only quoting it.
Kid stuck on one? You don’t just get the sheet.
The answer key prints on a separate page.
The arithmetic key pairs the ends rather than reciting n(a + l)/2. First plus last is the same as second plus second-last, all the way in — which is why the sum is that pair times half the count. A student who has seen the pairing can rebuild the formula; one who has only seen the formula cannot rebuild the pairing.
Every sheet starts at S₅ and the reason is the question rather than the difficulty: the first three terms are printed, so asking for S₃ is asking a child to add up three numbers already on the page. From five, the terms have to be generated before anything can be added.
One question from this sheet, worked through a step at a time.
S₇ for 5, 1, −3, …