Specific question: how can I improve on mentally performing calculations like these :
$$(78-59)\times23-8\%\times(270+130)$$
$$[2\text{digit}+-2\text{digit}]\times2\text{digit}+-x\%\text{of}[3\text{digit}+-3\text{digit}]$$
Without writing anything down. The thing is I can do the first part before the second minus pretty fast $19\times23=460-23=437$. When I move on to perform the second part $8\%\times(270+130)$ and I will come up with $32$ pretty fast but in the meantime I forgot the $437$ so I mess up.
I did found a technique that translates numbers into words; $437$ would become rmk=armaic or something like that. The technique is excellent for remembering numbers but in this case I would have to translate it back to perform the last calculation $(437-32)$ which slows me down.
So I was wondering if there are some faster techniques to perform this specific type of calculations (mind you I'm hoping to perform these kind of calculations in no more than $6$ seconds)