Answer:
Number of boys is 9
Step-by-step explanation:
Hint: number of girls added to number of boys must equal 27
27/3 = 9
boys: girls ratio is 1:2, so boys constitute 1/3 of the class
boys -> 1 x 9 = 9
girls -> 2 x 9 = 18
(to check, 9 + 18 = 27. If solution is still unclear, try drawing a pie of 3 equal components to represent a 1:2 ratio of slices)
