While playing basketball, nine-year-old marcus fell and broke his left arm. the arm was placed in a cast and appeared to heal normally. as an adult, marcus was puzzled because it seemed that his right arm is longer than his left arm. he measured both arms and he was correct his right arm is longer! how would you explain to marcus what happened?

If his right arm is  longer, this means that his left arm is shorter - so his injury must have somehow shortened his arm. It is possible that the left bone, although perfectly healed, is slightly bent as a result of the injury, making the arm shorter in the straight line. 

Also, some of the bone tissue might have been damaged and removed by the body slowly - putting the healthy bone parts together, resulting in a shorter bone.