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

Step-by-step explanation:

From the question,

The total number of marbles in the bag,n(S) =10.

The number of black marbles,n(B)=7

The probability that both marbles are red means that, the first marble is red and the second marble is red.

P(1st marble is Black)=

Since Petra picked the first marble without replacing it, the total number of the marbles will reduce by 1. Same is applied to the number of black marbles.

This implies that,

P(2nd marble is black)

P(both are black)=

54 kilometers per hour

step-by-step explanation:

according to rules:

1 km = 1000 meter

which means that 1 meter = 1/1000 km

1 hour = 3600 second [ as 1 hour = 60 min = 60 *60 seconds ]

which means that 1 second = 1/3600 hour

therefore, 1 kilometer/hour =

thus to convert 15 meter per second to kilometer per hour, we multiply 15 to 3.6 kilometer/hour.

15 meter/second=   which is the required answer.