To decrease an amount by 85% what single multiplier would i need to use?

You are asking about what number must you multiply another random number by to make that random number decrease by 85% of that random number, right?

If the above is correct, then the number is 0.15
because 100% - 85% = 15% and 15% = 15 / 100
= 0.15

Ithink it can be put them in order by 4 possible ways.that mean 3 group of 10 rocks,or an another group of 8 rocks.