function mean( N, K, n ) {
	if (
		isnan( N ) ||
		isnan( K ) ||
		isnan( n )
	) {
		return NaN;
	}
	if (
		!isNonNegativeInteger( N ) ||
		!isNonNegativeInteger( K ) ||
		!isNonNegativeInteger( n ) ||
		N === PINF ||
		K === PINF ||
		K > N ||
		n > N
	) {
		return NaN;
	}
	return n * ( K / N );
}
Returns the expected value of a hypergeometric distribution.

@param {NonNegativeInteger} N - population size
@param {NonNegativeInteger} K - subpopulation size
@param {NonNegativeInteger} n - number of draws
@returns {NonNegativeNumber} expected value

@example
var v = mean( 16, 11, 4 );
// returns 2.75

@example
var v = mean( 2, 1, 1 );
// returns 0.5

@example
var v = mean( 10, 5, 12 );
// returns NaN

@example
var v = mean( 10.3, 10, 4 );
// returns NaN

@example
var v = mean( 10, 5.5, 4 );
// returns NaN

@example
var v = mean( 10, 5, 4.5 );
// returns NaN

@example
var v = mean( NaN, 10, 4 );
// returns NaN

@example
var v = mean( 20, NaN, 4 );
// returns NaN

@example
var v = mean( 20, 10, NaN );
// returns NaN