Really easy to do
When put withsent＋ , and in negative form (〜ない), denotes that it is really easy to do. (literally: it requires no reasoning).
ここの試験に合格するのはわけない。 Passing this here test is really easy (it requires no understanding).
There is no way that I am able to (...)
中国語が読めるわけがない。 There’s no way I can read Chinese.
Sometimes, the が is left out. The meaning stays the same.
{微積分|びせきぶん}は分かる訳ないよ！ There is no way I will ever be able to understand differential calculus.
Must (...)
Similar to the must (not) forms, you can make it veryformal using わけ, making an expression denoting that something must (not) be done at all costs.
It's literally a more formal version of ～ては いけない.
Unlike with the must (not) forms though, it is いかない, not いけない!
今度は==負けるわけにはいかない==。 This time, i must not lose at all costs. (formal)
ここまで来て、==諦める訳にはいかない==。 after coming this far, i must not give up, whatever it takes. (formal)
http://guidetojapanese.org/learn/grammar/reasoning japanese.stackexchange.com - is わけない the shortened version of わけがない?