Hi
I always use a very simple method.
Take 10% as your anchor, if needed 1% as second anchor
I give you a couple of examples
- 157/533 then you calculate the 10% of 533=53. Then from 53 to 157 you aprox multiply by 3 -> then 30%
- 12/327 then you calculate the 10% of 327=33. But 33 higher than 12, so I take the second anchor (1%) 1% is 3.3. Now to get from 3.3 to 12 I multiply by a bit less than 4. So the percentage should be around 3.5%
Practice and it becomes easy!!
Cheers
Carlos