Lily and Elsa are both college students. Before mom gave them this months allowance lily had $750 and Elsa had &215. After mom gave each girl an equal amount of money for this months allowance, lily had twice as much money as Elsa. How much did mom give to each girl.

Mom gave $ 320 to each girl

Solution:

Given that Lily and Elsa are both college students

Before mom gave them this months allowance lily had $750 and Elsa had &215

So amount with Lily and Elsa already is:

amount with Lily = $ 750

amount with Elsa = $ 215

After mom gave each girl an equal amount of money for this months allowance, lily had twice as much money as Elsa

Let "a" be the equal amount of money which mom gave to Lily and Elsa

So now amount with Lily and Elsa after mom gave equal amount is:

amount with Lily = amount with Lily already + a

amount with Lily = 750 + a

amount with Elsa = amount with Elsa already + a

amount with Elsa = 215 + a

Now given that lily had twice as much money as Elsa

Amount with lily = 2 (amount with elsa)

750 + a = 2 (215 + a)

750 + a = 430 + 2a

2a - a = 750 - 430

a = 320

Thus mom gave $ 320 to each girl