[Grammar] use of his/her/their

[neelajah]

i have noticed in a English book mentioning that

someone lost their keys -wrong
someone lost his/her keys -correct

Could anyone clarify the usage of his/her/their with someone?

 

[Nightmare85]

I have noticed in an English book mentioning that

Someone lost their keys. - is wrong
and
Someone lost his/her keys. - is correct.

Could anyone clarify the usage of his/her/their with someone?

Welcome!

The problem is that someone can both be male and female.
In order to avoid this problem we use their.
Probably his/her is "more correct" althought I would never say that their is wrong.
Theoretically there are plenty of such examples:
Everybody has their own problems.
A person lost their cellphone last night.
Everyone wants to find their real love.

As you can see everybody is singular (because of has) but I use their, because I don't mean just male or female.

Maybe the "best" version would be:
Someone lost his or her keys.

Cheers!