Question

Dan and Paul share some money in the ratio 11:5.

Dan decides gives Paul £39 of his share to make the ratio 1:1.
How much did Paul originally have?

Answer 1

D = Dan's share

P = Paul's share

`\stackrel{D}{11}~~ : ~~\stackrel{P}{5}\qquad \implies \qquad \cfrac{D}{P}=\cfrac{11}{5}\implies D=\cfrac{11P}{5}`

now Dan decides to give Paul £39, so that means that Dan has £39 less whilst Paul has £39 more, so the new shares will be D - 39 and P + 39, and that puts them in a 1 : 1 ratio.

`\stackrel{D-39}{1}~~ : ~~\stackrel{P+39}{1}\qquad \implies \qquad \cfrac{D-39}{P+39}=\cfrac{1}{1}\implies D-39=P+39 \\\\\\ \stackrel{\textit{substituting from the 1st eqution}}{\left(\cfrac{11P}{5} \right)-39~~ = ~~P+39}\implies \cfrac{11P}{5}=P+78\implies 11P=5P+390 \\\\\\ 6P=390\implies P=\cfrac{390}{6}\implies \boxed{P=65}`