Question

There is a bag with only red marbles and blue marbles.

The probability of randomly choosing a red marble is 5/7
There are 30 red marbles in the bag and each is equally likely to be chosen.
Work out how many marbles in total there must be.

Answer 1

let the total number of marbles in the bag be x,

we have been given that :

• 
  `(5)/(7)th \: \: \: of \: \: total \: \: balls \: \: are \: \: red \: \:`

and total number of red marbles = 30

therefore, it satisfys the given relation :

• 
  `(5)/(7) * x = 30`

• 
  `x = (30 * 7)/(5)`

• 
  `x = 6 * 7`

• 
  `x = 42`

the total numbers of marbles in the bag = x = 42.