Final Answer:
As Bob's test increased from 75% to 90%, his grade increase by c. 20%.
Step-by-step explanation:
To answer this question, we need to calculate the percentage increase in Bob's test grade from 75% to 90%. To do this, we will follow these steps:
1. Determine the absolute increase of Bob's test grade by subtracting the initial grade from the final grade:
Absolute increase = Final grade - Initial grade
2. Calculate the percentage increase by dividing the absolute increase by the initial grade and then multiplying by 100 to convert it to a percentage:
Percentage increase = (Absolute increase / Initial grade) * 100
Now, let's calculate the absolute increase and percentage increase:
1. Absolute increase:
Absolute increase = 90 - 75 = 15
2. Percentage increase:
Percentage increase = (15 / 75) * 100
= (1 / 5) * 100
= 20%
Therefore, the percentage increase of Bob's test grade is 20%, which corresponds to option c. 20%.