Technically, it should be added to odds, not price, which is a conversion from odds anyway.

If one wishes to convert from price instead of odds, use $5.00 as the median.

We would then multiply all prices by 1.16
eg.
$5.00 x 1.16 = $5.80 (= 4.8/1)
Same as
4/1 x 1.20 = 4.8/1

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Cheers.