In a jar of marbles, the ratio of green marbles to black marbles is 3:5. If the jar contains 21 green marbles, how many black marbles are in the jar? green 3 21
black 5 ?

Your

10

12

30

35

there are 35 black marbles in the jar

Step-by-step explanation:

3*7=21

so..

5*7=35

yes. we do proportions in probabilities.

54 km / hours

step-by-step explanation:

we need to convert seconds to hours

60 seconds = 1 minutes

60 minutes = 1hour

15 m         60 second   60 minutes

  * *         = 54000 meters/ hour

second     1 minute             1 hour

now we need to convert meters to km

1000 m = 1 km

54000 m       1 km

*   = 54 km / hours

hour               1000m