Not getting correct answer on calculator

Question

My formula is

 

Squareroot (40)(1366) - (206)^2

 

Over

 

(40)(39)

 

The correct answer should be 2.7970 and I am positive these are the right numbers. It looks like I am  just having trouble writing it correctly on the calculator

Answer 1

The problem is that you have to be careful how you group the numbers.

 

The operation below will yield the correct answer.

 

=SQRT(((40)*(1366)-(206)^2)/(40*39))

 

We can simplify this a little as

=SQRT((40*1366-206^2)/(40*39))