Hello there. To solve this question, we'll have to use the data from the graph (dot plot) and determine the answers for each letter.
a) How many babies begin walking before 13 months of age?
For this, we have to add all the number of babies walking from the dot plot that are less than 13.
In this case, we add the values of babies walking with 9, 10, 11 and 12 months:
1 + 1 + 3 + 5 = 10
Therefore 10 babies have begun walking before 13 months of age.
b) What percent of babies begin walking at 12 months?
For this, we add the entire number of babies walking by age and calculate the ratio between the number of babies walking at 12 months and this result.
We have 25 babies at total and 5 of them began walking at 12 months of age, so now we take the ratio:
c) Which three ages combined account for less than 16% of the babies?
For this, we find how many is 16% of 25, that is, the total of babies:
So we have to find which three ages combined gives us less than 4 babies.
Notice we cannot choose the ages 12, 13, 14 because their number of babies, alone, are already bigger than 4.
We cannot also choose 11, because it is equal to 3 and all the other options are bigger than or equal to 1, so adding it with something else already would be equal to 4.
The same happens to 15 and 16, because their assigned value is 2, so adding both together gives us 4 and since all the others are greater than or equal to 1, we could not add other two together with them.
That's why the final answer is 9, 10 and 17, because they are the only numbers left that add up to 3 and this is a number less than 4, that is, less than 16% of the babies.