A bag has 10 mmarbles, and 7 are black. Petra picks 2 marbles without replacing the first. What is the probability that both are black?

The probability that Petra picks two black marbles, without replacing the first one is 7/15 or 46.7%.

Step-by-step explanation:

Let's recall the formula of the probability:

Probability = Number of favorable outcomes/Total number of possible outcomes,

therefore, the probability of picking a first black marble is:

P = 7/10

now, let's find out the probability for picking a second black marble:

P = 6/9

It's different than the first one because Petra did not replace the first one.

Now, the probability that both are black is:

P = 7/10 * 6/9

P = 42/90 = 7/15

The probability that Petra picks two black marbles, without replacing the first one is 7/15 or 46.7%

225x²+4=0

225x²=0-4

225x²=-4

x²=-4/225

x=±√-4/225

the answer is 62.8 cubic units