Conditional Multiplier

Hey guys,
I really need some help.
I am trying to create a document that will make claiming mileage easier.
The gov have a rule now that you can claim 40p a mile for the first 10,000 miles and 25p therafter. But you have to 'log' each trip seperately.
So I have created a sheet that calculates overall mileage based on each trip entered and puts the total into a cell (lets call it cell 'a'). I have done this by doing a simple column add.

What I want to do is have a cell for each trip made that shows the amount of miles travelled multilied by either 40p or 25p depending on if the total mileage is less than or more than 10,000 miles.

i.e. Target cell has a formula that says if cell 'a' is less than 10,000 the mileage entered in cell 'b' is multiplied by .4 to give a monetary value OR if cell 'a' is greater than 10,000 then the mileage entered in cell 'b' is muliplied by 25p to give a monetary value

i think thats wrong! that formula calculates every thing at 25p once over 10000
so 19,000
returns £4,750

since its 40p up to 10000 then 25p there after surely it should be
£6250
10000@ 40p =4000
9000@25p=2250

=MAX((A2-10000)*0.25,0)+MIN(A2,10000)*0.4
otherwise if you did 10001 miles youd get £2,500.25
which is less than the 4000 for 10000 !