Hello : the consecutive room numbers are : n , n+1 n(n+1) =420 n²+n -420 = 0 the discriminant delta = b² - 4ac ( a = 1 and b = 1 and c = - 420 delta = (1)²-4(1)(-420) =1681= 41² n = (-1 -41)/2 ( refused negatif number) or n = (-1+41)/2 =20 <span> the room numbers.are : 20 , 21</span>
