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## Homework Statement

Find the total gravitational potential energy of the three masses.

## Homework Equations

U=-GMm/r

## The Attempt at a Solution

U between the 10 kg mass & the 20kg mass

-(6.67*10^-11)(20kg)(10kg)/.20 m = -6.67 * 10 ^-8 J

U between the 20kg mass and the 5 kg mass

-(6.67*10^-11)(20kg)(5kg)/.10m = -6.67*10^-8 J

U between the 10 kg mass & the 5 kg mass

-(6.67*10^-11)(10kg)(5kg)/.2236 m = -1.49 * 10^-8 J

adding them up I got -1.483*10^-7 J

but the back of my book says -1.96 * 10^-7 J

Am I doing something wrong?