function mean( n, p ) {
	return addon( n, p );
}
Returns the expected value of a binomial distribution with number of trials `n` and success probability `p`.

@private
@param {NonNegativeInteger} n - number of trials
@param {Probability} p - success probability
@returns {PositiveNumber} expected value

@example
var v = mean( 100, 0.1 );
// returns 10.0

@example
var v = mean( 20, 0.5 );
// returns 10.0

@example
var v = mean( 20, 1.1 );
// returns NaN

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