Thank you for the opportunity to help you with your question!
Total number of marbles = 5+4+7+9 = 25
First draw - Probability of selecting a blue marble = 7C1/25C1 = 7/25 Second draw, Probability of selecting a yellow marble = 9C1/24C1 = 9/24 .................)as now total number of marbles is 24) Third draw, probability of selecting a red marble = 4C1 / 23C1 = 4/23
The probability of all three events to happen together is = (7/25)*(9/24)*(4/23) = 21/1150 Please let me know if you need any clarification. I'm always happy to answer your questions.