Video: Patterns of Triangle Numbers

Daniel is making dots that look like triangles. The rule for the number of dots to use is add one more dot than you added before. How many dots will be in the next triangle?

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Video Transcript

Daniel is making dots that look like triangles: one dot, three dots, six dots, 10 dots: add two, add three, add four. The rule for the next number of dots to use is add one more dot than you added before. How many dots will be in the next triangle?

The question tells us there are 10 dots in the last triangle. We have to work out how many dots would be in the next triangle. The question also tells us we need to add one more dot each time. First, we added two. Then we added three. Next, we added four. So then we need to add five. Five is one more than four. 10 plus five is 15, so there will be 15 dots in the next triangle.

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