// params = value, count, value, count, ...
static double weightedAverage_lit(double... params) {
  double total = 0, sum = 0;
  for (int i = 0; i < l(params); i += 2) {
    double weight = params[i+1];
    sum += params[i]*weight;
    total += weight;
  }
  ret doubleRatio(sum, total);
}