"I have four forks and four knives."
Translation:יש לי ארבעה מזלגות וארבע סכינים.
I must remember: knife is ambiguous and fork is masculine with a femenine ending... Thaks a lot. Cheers!
It's one of the words that are irregular. Like bird, tsipor, it is female but plural is male ending. There is a list and this has been discussed on a few of the discussions. To search them go to duolingo.com , make sure your browser is in desktop view /mode. If you don't see discussions on the top as an option you aren't in desktop mode but mobile mode. (You don't have to be on a computer for desktop view, but you usually have to change your browser setting on a smart device as it's usually set to mobile view).
You can also go to a link someone has provided before https://www.safa-ivrit.org/irregulars/pluralml.php
In the future you can also search morfix. Or a really helpful site I've found is wiktionary.org/ then just put in the Hebrew word and it'll (usually) give you what gender it is. For verbs there's Pealim.com