3. Divide 5 boys and 3 girls into three groups, with each group having at least 1 boy and 1 girl. Then there are a total of different grouping methods.
3. 150 .

According to the problem, there are two possible distributions of the number of boys in the three groups. If the number of boys in the three groups is 1, 1, and 3, respectively, then there are $\frac{C_{5}^{1} C_{4}^{1}}{2!} 3!=60$ ways; if the number of boys in the three groups is 1, 2, and 2, respectively, then there are $\frac{C_{5}^{1} C_{4}^{2}}{2!} 3!=90$ ways.
In total, there are 150 ways.