Consider a table
tab = Table[{i,i^2,i^3,i^5,i^0.3,i^0.7},{i,0.2,3,0.1}];
I would like to multiply the 2rd and 5rd columns by some number. This is how I do it:
a = 2
{#[[1]],a*#[[2]],#[[3]],#[[4]],a*#[[5]],#[[6]]}&/@tab
However, such syntax becomes really annoying if the table would have many columns:
{...,a*#[[K]],...,a*#[[M]],...}&/@tab
where K,M are some numbers. How can I multiply the columns in a more compact way? I.e., what is an analog of ... in Mathematica?