how can I generate n random numbers whose summation will be around 1?

You can try the Dirichlet distribution ( http://en.wikipedia.org/wiki/Dirichlet_distribution#String_cutting and https://statipedia.org/wiki/index.php?title=Dirichlet)

You need to specify more details about how they're distributed, using only the sum-constraint condition allows too many possible distributions over parameters. The Dirchlet is a commonly used distribution which satisfies this property

How can I generate n random numbers whose summation will be around 1?

You can try the Dirichlet distribution (see also, https://statipedia.org/wiki/index.php?title=Dirichlet).

You need to specify more details about how they're distributed; using only the sum-constraint condition allows too many possible distributions over parameters. The Dirichlet is a commonly used distribution which satisfies this property.