Question

A jar contains 8 white marbles, 10 orange marbles, and some red marbles. If the probability of picking a red marble is 1 in 4, then how many red marbles are there?  
[4 MARKS]

Answer 1

Let the number of red marbles be x
Total no. Of marbles = 10+8+x
=18+x
P (red marble) = x/18+x
1/4=x/18+x
4x=18+x
3x=18
x=6
The total no. Of red marbles is 6

Answer 2

Let the no. of marbles be x .

$\tt \dfrac {x}{8+10+x} = \dfrac{1}{4}$

4x = 8 + 10 + x

3x = 18

x = $\tt \dfrac {18}{3}$

x = 6