Gravitational field strength between masses

[calculator20]

Homework Statement

A mass at a point X gives rise to a gravitational field strength g at point P as shown. An identical mass is placed at point Y

x ________ p ______________________ y

The resultant g f s is now?

Homework Equations

g = Gm/r2

The Attempt at a Solution

I know the answer is between g and zero but don't know if my method is correct?

I'm assuming distance x to p is r and p to r is approximately 2r

Am I right that g = Gm/r2 - Gm/2r2 so g is approximately 1/2?

 

[haruspex]

I'm assuming distance x to p is r and p to r [correction: y] is approximately 2r

Am I right that g = Gm/r2 - Gm/2r2 so g is approximately 1/2?

Write out Gm/2r2 more carefully (using parentheses) and you might spot your error.