Percentages in solidity

Question

How would i work out "x is what percent of y" or for example 5 is what percent 10 = 50%. For some reason i just cant wrap my head around it.

A clip of my code is below, i want to work out balanceOf[msg.sender] is what percent of totalCrowdFund.

 uint256 public totalCrowdFund;
bool refundStatus;

mapping(address => uint256) public balanceOf;
mapping(address => bool) public emergencyRefundStatus;

constructor() {
    owner = msg.sender;
    totalCrowdFund = 0;
}

Answer 1

I suspect that the percentages can be very small, so the formula is as follows:

uint256 res = balanceOf[owner] * 100000 / ( totalCrowdFund);

where the result is 1/1000 percent. That is (res = 267) == 0.267%