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 :

• $\dfrac{5}{7}th \: \: \: of \: \: total \: \: balls \: \: are \: \: red \: \:$

and total number of red marbles = 30

therefore, it satisfys the given relation :

• $\dfrac{5}{7} \times x = 30$

• $x = \dfrac{30 \times 7}{5}$

• $x = 6 \times 7$

• $x = 42$

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