How many individuals who were being tracked and who were less than 30 years of age in 1980 survived until 2020?
Explanation:
Those who were less than 30 years old in 1980 will be less than 70 years old in 2020.
∴ Number of people alive below 70 in 2020 = 140 + 100 + 125 + 105 = 470
Hence, option (b).
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