We can’t do floating point maths in Solidity. But calculating percentages does not require floating point math.

A quick example is shown below, based on https://ethereum.stackexchange.com/questions/52781/division-percentages-in-solidity-a-workaround

    function getPercent(uint part, uint whole) public pure returns(uint percent) {
        uint numerator = part * 1000;
        require(numerator > part); // overflow. Should use SafeMath throughout if this was a real implementation especially on older versions of Solidity
        uint temp = numerator / whole + 5; // proper rounding up
        return temp / 10;
    }

Also see my page on floating point math in Solidty

This post is incomplete and a work-in-progress
I'll update it soon and flesh it out with more info!

Spotted a typo or have a suggestion to make this crypto dev article better? Please let me know!