Part (a)
Count the number of individual digits in the leaf category only.
For the first row, we have 3 leaves representing 3 different ages between 20 and 29. Specifically those ages are 26, 26, 29. Repeat ages are possible.
The second row has 17 leaves in it
So far we have 3+17 = 20 people accounted for.
Keep this process going until you get every row.
You should find that in total there are 56 leaves in all to represent the 56 signers of the declaration of independence.
To verify the answer, you can look it up on any history website dealing with this point in time.
Answer: 56
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Part (b)
The youngest age is 26 because it corresponds to the smallest stem (2) and the smallest leaf (6)
Answer: 26
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Part (c)
The oldest person on the other hand was 70 since we look at the largest stem (7) and the largest leaf of that stem. There's only one leaf here so we don't have to worry about the second aspect.
Subtract the oldest and youngest ages to get the range.
range = max - min = 70 - 26 = 44
There's a 44 year gap between the oldest and youngest person.
Answer: 44
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Part (d)
No, the majority weren't between 30 and 39. Instead, the majority of the signers were between 40 and 49 since we have the most leaves in the stem corresponding to "4".