Question

The sum (S) of the first x multiples of 10 is given by S=5x(x+1). Use the rule to show that 10+20+30=60

Answer 1

how many multiplies of 10 do you have in that sum 10 + 20 + 30 ?

Answer 2

multiplies >.< multiples*

Answer 3

3

Answer 4

correct. So if S is the sum of the first "x" multiples of 10, where x is a number, it would make sense that if we wanted to add the first 3 multiples of 10, we should let x = ....

Answer 5

3

Answer 6

right again. So in that equation 5x(x+1), let x = 3, and you are done. Just how that when you plug in x = 3, that 5x(x+1) becomes 60.

Answer 7

show*

Answer 8

Thanks heaps! You made that so easy to understand!