The number of degrees in one acute angle of a right-angled triangle is equal to the number of grades in the other; express both the angles in degrees. So I have found the following answers : 810/17=47,05... degrees and 810/17=47,05... grades which gives 42,35... degrees Now, the real answer is the following : 900/19=47,3... degrees and 900/19=47,3... grades which gives 42,63... degrees The only problem with my answer is the following : 810/17degrees=900/17grades so : 900/17 grades+ 810/17 grades = 100,5.. grades (but for the rest, everything is fine, I get get 90 degrees perfectly and respect all conditions.) Would you count this as an error ??? Here's what I did : (Help me see the error) x degrees= (x+x/9) grades x grades= (x-x/9) degrees so.. x degrees+(x-x/9)degrees=90 degrees 17x/9 degrees=90 degrees 17x=810 x=810/17 degrees By the formulaiton of the problem, we also have 810/17 grades Conversion 810/17 degrees=(810/17+(810/17)/9) grades=900/17 grades and 810/17 grades=(810/17-(810/17)/9) degrees= 720/17 degrees Can somebody tell me where I went wrong ??? (By the way, I see how to obtain the "real" answer, but I don't see why mine would be wrong ...) Thank you !