There are only blue cubes,yellow cubes and green cubes in a bag.There are twice as many blue cubes as yellow cubes and four times as many green cubes as blue cubes.Hannah takes at random a cube from the bag.Work out the probability that Hannah takes a yellow cube

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Let us translate the sentence into mathematics step by step:
There are twice as many as blue cubes as yellow cubes
2 x yellow = 2 cubes = blue         
1 cube = yellow 

There are four times as many as green cubes as blue cubes
4 x 2 ( blue cubes ) = 8 cubes = green

Total cubes = yellow + blue + green
                    =      1      +   2    +    8
                    = 11 

Hannah takes random cube
Probability that Hannah takes yellow cube:
P = number of Yellow cubes ÷ Total number of cubes
P = [tex] \frac{1}{11} [/tex]