It is -10 because any time you multiply (or divide) a positive by a negative it will always be a negative number. My teacher taught me to use a triangle. Two negatives and 1 positive. Cross out the symbol that is being used in the problem, whatever is left is if your answer is a positive or negative :) this doesn’t work for add or sub though.
So 2•5 is 10 of course now there is 1 negative and 1 positive you have - - + you have one negative so thay leaves you with - + You have one positive so that leaves you with -
