Take 1.724 = (1+r)*5 and divide both sides by 5.

1.724/5=1+r

now, subtract 1 from both sides

(1.724/5)-1=r

I don't get 1.1164 either... You're sure you have it right?

You have to know the value of r and then you follow the maths laws of multiplication.division , addition and subtraction in that order
so 1.734 = the sum of 1+r, multiplied by 5