Hi, a new gre student here. I just finished the quiz for Finding number of numbers in factorial (prepswift) , and got the question on finding the number of 2s in 10! wrong. Acc to the formula on video, we should do (last multiple - first multiple) / 2 then +1, which comes out to (10-2)/2 +1 = 5. Then we add number of multiples of 2^2 and 2^3, which is 1 each… which comes out to 7. But then when you count the number of 2s in the actual 10!, it’s 8… what am I getting wrong here? Anyone can help me?

Hey, your calculation for multiples of 2^2 seems to be wrong.

It should be (8-4)/4 + 1 = 2, thus, 5 + 2 + 1 = 8.

Also, we can see that 4 and 8 both have one 4 each, hence 10! would have 2 2^2.

OH you’re right. I totally forgot 8 would also have a 2^2. Thank you!!! Super helpful.