// Add your functions below:
function validateCred(numArr) {
  let total = 0;
  for (let i = numArr.length - 1; i >= 0; i--) {
    let currValue = numArr[i]
    if ((numArr.length - 1 - i) % 2 === 1) {
      currValue *= 2;
      if (currValue > 9) {
        currValue -= 9;
      }
    }
    total += currValue;
  }

  return total % 10 === 0;

}