A juice bar sells apple juice for $5$ dollars per cup, orange juice for $3$ dollars per cup, and peach juice for $10$ dollars per cup. In this year's summer sale, the bar decides to make a blended fruit juice by mixing up $30$ cups of apple juice, $50$ cups of orange juice, and $20$ cups of peach juice. If the size of the cup doesn\textquotesingle t change, how much will a cup of blended fruit juice cost on average? 
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