A1.90-m-long barbell has a 25.0 kg weight on its left end and a 37.0 kg weight on its right end. if you ignore the weight of the bar itself, how far from the left end of the barbell is the center of gravity?

To solve for the distance from the left end of the barbell:37 * 1.9 = ( 37 + 25) * x x = 37*1.9 / (37+20) = 1.23333 m 
Additional info: if we are going to repeat this with a uniform bar of mass 9kg whose center of mass is 0.75 m from the left, the answer would be
37 * 1.9 + 9 * 0.75 = (37 + 25+ 9) * y y = (37 *1.9 + 8 * 0.75) / (37 + 25 + 9) = 1.07 m