how to calculate assumed mean ?

how come the assumed mean 10 in the 1st video of variance and step deviation?

Here is the link for answer to assumed mean.

https://www.meritnation.com/ask-answer/question/what-is-assumed-mean-how-can-we-find-it/statistics/1571984

In the video, we have taken assumed mean = 10.

We can assume any value as mean. The answer will not change. But we prefer the central value to be the assumed mean.