I got most of them right doing them in my head, which is amazing to me since growing up, I had to go to summer school for many years for math, and never got better than a C, and that only once.
My parents tried getting me a tutor and everything (Some poor Electrician’s Mate looking for some extra money!) but nothing worked.
When I graduated high school, I couldn’t add or subtract fractions. I had a major mental block with it.
It stayed that way until I took a college level math course in the USN and got personal tutoring from a civilian on the ship I was working with on a project.
At the time, I read a book that taught me how to do figures in my head.
For example, if the problem is 43 x 25, I do 10 x 25 = 250, multiply that by 4, and then add 3 x 25.
That I can do that type of thing in my head is a source of never-ending pride, considering how badly I suffered at math as a kid...:)
That’s exactly how I did the problems about “odd” numbers in my head. Break them up into smaller parts basically and add up the simpler sums. It’s the best way to do such problems mentally I think.