Question

Why we say muchas gracias and not mucho gracias?

differences between mucho and muchas and when we use it??​

Answer 1

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Answer 2

Saying "mucho gracias" is grammatically wrong, so she was right for correcting you. Gracias is a feminine noun, and it's also plural. Mucho is an adjective. Adjectives should always match noun's gender and number, so it should be muchas → muchas gracias.

Step-by-step explanation:

Hope it helps