Innaccurate values

[Chubbs]

Hello,
I'm having trouble getting my program to send back accurate values. It works, but is inaccurate, especially with values of 10 or 1000. If I have grade 1 equal to 10 and the rest of the values to 100 the result will still be 54 instead of 51.3. What do I have wrong?

#include <iostream>
using namespace std;
int main ()
{
	double x, a, bgrade;
	cout << "BASAL Gradebook:" << endl;
	for (x = 1; x <= 18; x++)
	{
		cout << "	Enter BASAL grade #" << x << " (out of 100): ";
		cin >> a;
		bgrade = 3 * (a / 100) * 18;
	}
	cout << "BASAL points earned: " << bgrade << endl;
	cout << endl;
}

[Moschops]

bgrade is replaced every time you go round the loop, so if the last grade entered is 100, the result will be 54. The previous 17 results have no effect.