1/5 + 3/10 = 1/2 when simplified. So half of her flowers are yellow and the other half is red and white. Sence Lauren has 18 yellow flowers then there must be a total of 18 red and white flowers. So 18 + 18= 36.
The lowest common denominator of the two fractions is 4 because it is the smallest number that both fractions can be transformed into. 3/2 is multiplied by 2 to create 6/4 which can be added to 11/4.
