Specifically, problems that are in the format of (xx)*(yy)+(abc) for e.g 67*35+667
Currently, it takes me an average of 45 seconds to perform these type of problems in my head. Although, I only end up being right 50% of the time.

Using the example I wrote about, I'll describe the method I use while solving these equations.

First I'll break down 67*35 into 67*30 + 67*5

Then I'll multiply 67*3 by further breaking it down into (60*3)+(7*3) which computes to 201. Then I'll add a 0 at the end making it 2010.
I'll calculate 67*5 by basically halving 67, kind of like 60/2 + 7/2 = 335

I'll then add 335 to 2010 by adding 300 first, then 30, then 5).
Which is 2345.

Finally, I'll add 667 to it by adding 700 to it, then subtracting 33 (which I compute by subtracting the last digit (7) from 10, and the subtracting it's preceding digit (6) from 9.

Now, my questions:

1. Are the some ways that can help me solve these problems faster?

2. How do I fuck up less while solving these types of problems?