Answer:
There are 45 boys.
Explanation:
The best way to easily solvethis is by making equations, see below.
![let \: b \: represent \: number \: of \: boys \\ let \: g \: represent \: number \: of \: girls](https://img.qammunity.org/2021/formulas/mathematics/high-school/940lhn1hk2cffih6v8hf80gp5yq362zdlj.png)
![b + g = 120 \\ b = (3)/(5) g](https://img.qammunity.org/2021/formulas/mathematics/high-school/phw5twjvw07qj1jxz76tm002df8cry21k2.png)
Now we can subtract the secons equation from the first.
![g = 120 - (3)/(5) g](https://img.qammunity.org/2021/formulas/mathematics/high-school/kk1rr2vt8800dgvae8lz3680yhnty5cith.png)
I'm also goong to multiply the equatipn by 5 to remove the fraction.
![5g = - 3g + 600](https://img.qammunity.org/2021/formulas/mathematics/high-school/dl8f0tecd4xbgee9s8ixvh63tqkxpelilz.png)
Now simplify
![8g = 600 \\ g = 75](https://img.qammunity.org/2021/formulas/mathematics/high-school/9xstuc2bnmee6wrcyzoqocx2zzpijkgnrb.png)
Now we found out there are 75 girls. Now we insert this into our second equation to find how many boys there are.
![b + 75 = 120 \\ b = 45](https://img.qammunity.org/2021/formulas/mathematics/high-school/y6q2ycuuklch1v4utlia9oa0l3tprbvf21.png)
Now we know there are 45 boys.