How would you solve this mathematical problem?

How would you solve this mathematical problem?

https://kimmonesittely.blogspot.com/p/145-how-would-you-solve-this.html

https://fi.newsner.com/uutiset/osaatko-ratkaista-taman-tehtavan-oikeita-vastauksia-on-kaksi-mutta-melkein-kukaan-ei-saa-sita-oikein/


Here is one mathematical formula, or the problem what solution is based on the thing, that the maker of this test must find the formula. This problem is taken from the "Newsners" home page, and it is published on Facebook.

As you see there might be two or three solutions, depending on what system the solution maker want to use. The examination is on the page, what is linked below this text, and simplest way is just plus the numbers if the last line, and the answer would be 19, but that would not follow the formula, what is in the problem.

1+4=5
2+5=12
3+6=21
8+11=x

There might be an answer that the last number of the problem would be multiplicate the last number with the line order number, and that thing can demonstrate by using the plus mark. That means that the solution for this mathematical problem would get by using the next formula.

1+4=5
2+5+5=12
3+6+6+6=21
8+11+11+11=41

The source homepage answer you might read from the next link, and that is also the source of this problem. As you might see, there could be many ways to solve mathematical problems. The answer is taken that the last number of each line would plus to the next line. And you might see that would also give the correct answer for that formula.

https://fi.newsner.com/uutiset/osaatko-ratkaista-taman-tehtavan-oikeita-vastauksia-on-kaksi-mutta-melkein-kukaan-ei-saa-sita-oikein/

1+4=5
5+2+5=12
12+3+6=21
21+8+11=40