I have a question that I believe I can solve but somehow I'm not getting the correct answer. So I'd really appreciate if anyone can point out my mistake for me.

The question is:

The grades of 1st year students were analysed. 70% of the top one quarter of the 1st year had been in the upper 10% of their school, as had 50% of the students in middle half of the 1st year and 20% of the students in the bottom quarter of the 1st year.

a) What is the probability that a randomly chosen 1st year student was in the top 10% of his or her school?

(There are parts b. and c. too but I guess this one is the key.)

My attempt:

I made this table first.

......................Top 10%...Not 10%.....Total

Top Quarter.......0.175.......0.075.........0.25

Mid Half.............0.25.........0.25..........0.5

Bottom Quart......0.05.........0.2...........0.25

Total..................0.475.......0.525..........1

So my answer to the question is 0.475. However, the correct answer given is 0.4875.

Please please help if you can!! I'll be eternally grateful.

Thank you in advance.