将进价当做单位“1”,设破裂的西瓜有x个,则未破的有1000-x个,由此可得方程:(1-30%)x+(1000-x)(1+40%)=1000×(1+28.8%). 0.7x+1400-1.4x=1288, 0.7x=112, x=160.答:破裂了160个西瓜.故答案为:160.