When a number is decreased by 30% of itself, the result is 28. What is the number?

Question

I know that I divide 240/65 and I know my answer is 369.23. But I just want to know how do I know where to put the decimal in my answer. How do I know it goes after the 9 in 369.23?

Answer 1

let x be unknown number then 30% of x is .3x

x-.3x=28

.7x=28

x=28/.7= 40