Most people struggle with big numbers with a lot of zeroes. Here's how I teach my students and I've gotten great results w/ it.
The thing to remember is: 1000 = K, 1000,000 = M, and ... so on for "B"). Now,
K * K = M, M*K = B, B/M=K, B/K=M. Take a minute to absorb this.
Next, do some practise. What is 2million divided by 10 thousand? That's 2M/10K = 0.2 * (M/K) = 0.2K == 200.
Do another one: what is 80B divided by 40K? 80/40 = 2, and B/K = M, so 2Million.
It gets easier: do the following in your head:
- 90,000 / 4500
and so on.. of course, things aren't as easy for fractions, etc but most errors happen due to these trailing zeroes and this method takes care of that.