Explain why it is important to put a lid on the petri dush

You have to put a lid on petri dishes in order to ensure that no outside contaminants get inside the dish.

there are 35 white marbles

step-by-step explanation:

y- yellow marbles

4y + 5 = 45

subtract 5 from both sides

4y = 40

divide for from both sides

y = 10

plug in 10 to get 40 yellow marbles then subtract by 5 to get 35 marbles

thus there are only 10 yellow marbles