Question 51253
Let x represent the first multiple of 10 (i.e., 10x).  The next two consecutive multiples of 10 become 10(x+1) and 10(x+2).  So our equation becomes {{{(10x+10(x+1)+10(x+2))/2=75}}}.  Now we just expand and simplify to solve.  We first get {{{(10x+10x+10+10x+20)/2=75}}}.  Combining like terms produces {{{(30x+30)/2=75}}}, which simplifies to {{{15x+15=75}}}. Subtract 15 from both sides:  {{{15x-15=75-15}}}, which simplifies to {{{15x=60}}}.  Now divide both sidess by 15:  {{{15x/15=60/15}}}, which simplifies to {{{x=4}}}.  That means the first number is 4*10, or 40; the next number is 10(4+1), or 50, and the next number is 60.  Adding 40+50+60 produces 150; dividing 150 by 2 produces 75.  That completes our check of our answer, which means our answer of 40, 50, and 60 is correct.