binomial distribution question query

Looks like a typo as they define and use it as the 12 outcomes 0,1,2, ...,,11 so it should be P(x<12)

oh ok thank you. Would you mind helping me with one more question, a different one?
Its the practice question 1 - in the mark scheme they got k as 1/10 whereas I got 1/4. I don't know where I went wrong. I used the cumulative distribution function,

Can you upload what you did.

i dont have any storage left to upload the picture. is it ok if you just briefly explain how to do the question?

Shouldn't be more than a oouple of lines. Just upload your attempt as text.

so i thought that X has to be 4 or less so I did P (X<=4) = 1 getting k as 1/4. so i really don't get how they got 1/10

P(x<=4) is not P(x==4).
Just sum the given probabilities?

why sum them?

Because P(X<=4) is the sum of each of the probabilities P(x==1) to P(x==4).