There are 65 students in a science club. 40% of them bought a club t-shirt with a picture of albert einstein. how many einstein t-shirts were purchased?
a. 20
b. 24
c. 25
d. 26

So in order to solve the question, you must find out what is 40% (or 40/100) of 65 students. To do this you use the following equation:

65(students) X 40/100= number of students that bought a t-shirt.
26 students bought a t-shirt, so 26 shirts were purchased
ANSWER: D. 26

First, imagine that if there were 100 students in the science club in total, there would be 40 students who want to buy the T-shirt. That's what the number 40% tells us.
65 students in total* ( 40 students buying T-shirts/ 100 students in total)= 26 students buying T-shirts.
Note that students in total (in 65 students in total) and students in total (in 100 students in total) cancel out, and each student only buys one T-shirt.
Thus the final answer is D. 26
Hope this would help :))