Common Core: S-ID.4
Problem 7 of 45s12-007
Hand lengths of adults are approximately normal, mean 18 cm, SD 1.2 cm. What proportion are longer than 19.5 cm? Area left of : ; left of : .
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Solution walkthrough2:01
- Turn 19.5 cm into a -score: how many SDs it is above the mean. The table gives the area to the left of .
- Subtract the mean, then divide by the SD: .
- The question gives the area to the left of : . That is the share of hands shorter than 19.5 cm.
- Longer than 19.5 cm is the right tail. The whole area is 1, so the tail is .
- Traps: is the left side, skips dividing by the SD, and is only mean to 19.5.