12) E

Mean number of steps (line in the box) = 50% = 850
Upper quartile value = 75% = 1000 steps

Percentage difference = 75 – 50 = 25%
So 25% (¼) of the people have taken steps between 850 and 1000.

Probability of first person being within the range = ¼
Probability of second person being within the range = ¼
Probability of third person being within the range = ¼

Probability of all three members being within the range = ¼ x ¼ x ¼ = ⅟₆₄