Conditionally format % based on value of another cell

[The Grim Discovery]

People,

Please lend a hand. I want B1 and then C1 to conditionally format with a green fill if they equal 90% or more of cell A1.
Looking around I thought this formula I found would (for cell B1) do it

=(B1/A1)>=0.9

But it didn't format. And I cant figure it.
As ever, thanks

[TABLE="class: outer_border, width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]A[/TD]
[TD]B[/TD]
[TD]C[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]10[/TD]
[TD]9[/TD]
[TD]5[/TD]
[/TR]
[TR]
[TD]2[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

 

[Scott T]

That works for me. When you put the formula in a cell do you get true?

Excel 2010
	A	B
1	10	9
2
3		TRUE
Sheet1

Cell Formulas
Range	Formula
B3	=(B1/$A$1)>=0.9

 

[The Grim Discovery]

Thanks for responding Scott and confirming the formula was alright. Turns out the cell was 'text'. Schoolboy error. Cheers.