In Hindi, each letter is spoken with an inherent sound 'a' with it.
But in this case, we omit the inherent vowel sound 'a' in the middle of the word
1. When two letters are joined together as in नाश्ता (nashta), वर्ष(varsh), पुस्तक(pustak)। 'sh', 'r' and 's' sounds do not have vowel sound in those words respectively.
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