protected function exchangeRates($baseCurrency, $defaultCurrency, array $currencyRates)
    {
        $precision = 5;
        $defaultCurrencyRate = round(1 / $currencyRates[$defaultCurrency], $precision);

        $exchangedRates = array();
        $exchangedRates[$baseCurrency] = $defaultCurrencyRate;

        unset($currencyRates[$baseCurrency], $currencyRates[$defaultCurrency]);

        foreach ($currencyRates as $currencyName => $rate) {
            $exchangedRates[$currencyName] = round($rate * $defaultCurrencyRate, $precision);
        }

        return $exchangedRates;
    }