maths question

I should be able to work this out but am stumped !!!
If I can claim tax relief of 100% the first 96 days of the year and then only claim 75% for the remaining 269 days of the year. What is the averaged % I can claim for the whole 365 days of the year.

I have been told that the answer is 81.5%, but I cant figure out how calculate it ???

269/365 * 75% + 96/365 * 100% = 81.5%

Check if your interest statements are worked out on a monthly/quarterly basis as there was a big drop in interest rate around the time of the change and it may be more benificial to work out the calculation on a quarterly basis.