Answer :

[tex]x+y=300\$ \\\\ x;y \ \ directly \ proportional \ \\ 3;7 \\\\ \frac{x}{3}=\frac{y}{7}=k \\\\ x=3k \\ y=7k \\\\ 3k+7k=300\$ \\\\ 10k=300\$ \\\\ \boxed{k=\frac{300}{10}=30\$} \\\\ x=3*30\$ \\\\ \boxed{\boxed{x=90\$}} \\\\ y=7*30\$ \\\\ \boxed{\boxed{y=210\$}}[/tex]
Dividing £300 in ratio 3:7.

First add the ratio: 3+7 = 10.
So in all there should be 10 parts.

For the value of 3,  the share would be =  3/10 * 300 = 90

For the value of 7,  the share would be =  7/10 * 300 = 210

Therefore in the ratio of 3: 7 =   £90 and £210.

Cheers.