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EXACT MATCH: When placing a primary keyword in the first 100 words is it okay to add ‘in’?

On my Home page my Primary Keyword is Chiropractor Melbourne. When placing the primary keyword in the first 100 words of my content can I use Chirpractor in Melbourne as this flows and reads better? or does the primary keyword have to be exact?

No, it doesn’t not have to be exact in the body copy.
Try to keep it exact in the title tag, image alt and image file name.