Final answer:
To calculate the number of fifth graders who signed up for an after-school activity, multiply the total number of fifth graders by the percentage who signed up, which gives us 120 students.
Step-by-step explanation:
To find out how many fifth graders at Brenham Middle School signed up for an after-school activity, you would multiply the total number of fifth graders by the percentage that signed up. Since 40% of the 300 fifth graders signed up, you would calculate 40% of 300.
First, convert the percentage to a decimal. 40% as a decimal is 0.40. Then, use the decimal to find 40% of 300 by multiplying:
0.40 × 300 = 120 students.
Therefore, 120 fifth graders signed up for an after-school activity at Brenham Middle School.