Mario makes 6 free throw shots out of his first 10 attempts. What is the least number of consecutive shots Mario must make to increase his overall percentage from 60% to at least 70%?

After making n consecutive shots, Mario will have made 6 + n out of 10 + n attempts. To reach at least 70%, solve (6 + n)/(10 + n) ≥ 0.70, which gives 6 + n ≥ 7 + 0.7n, so n ≥ 3⅓. Since he must make a whole number of shots, the least number is 4: choice B, 4 shots.

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