Yes, that is perfect English. You can also say, "I don't know whether it will rain tomorrow." In American English, you can also say, "I don't know whether/if it's going to rain tomorrow." All of these mean exactly the same thing. :)
5 mei 2015
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Yes even your punctuation is good
5 mei 2015
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Heb je je antwoorden nog steeds niet gevonden?
Schrijf je vragen op en laat de moedertaalsprekers je helpen!