He grows six inches a year because 12 x .5 = <<12*.5=6>>6

He will grow 24 inches between his 8th and 12th birthday because 4 x 6 = <<4*6=24>>24

He will be 74 inches tall because 50 + 24 = <<50+24=74>>74

# Answer

74
<|im_start|>system
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<|im_start|>user
Alexander was 50 inches on his 8th birthday. If he grows 1/2 a foot a year, how many inches tall will he be on his 12th birthday?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
74
Alexander was 50 inches on his 8th birthday. If he grows 1/2 a foot a year, how many inches tall will he be on his 12th birthday?
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