from 6.5 to 4.8

Are you looking for the percent of decrease?

yes

6.5 - 4.8 = 1.7

Divide 1.7 by 6.5

I thought I had to multiply 1.7 times 100 the divide that by 6.5

You can do it either way.

1.7/6.5 = 0.2615 = 26%

wouldn't it be 26.1?

If you round to the nearest whole number it is 26%. If you round to the nearest tenth of a percent, it's 26.2%.