Question 1135510
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You have received 3 responses, all showing the same formal algebraic solution.<br>
Solving problems like this mentally is good exercise for the brain.  Here is a simple informal solution using logical reasoning and some simple arithmetic.<br>
Lilly starts with $750 and Ellsa with $215; the difference is $535.<br>
Their mother gives each of them the same amount, after which Lilly has twice as much as Ellsa.<br>
Since they both received the same additional amount, the difference between their amounts is still $535.<br>
If Lilly now has twice as much as Ellsa, and the difference between their two amounts is $535, then Ellsa has $535 and Lily has 2*$535 = $1070.<br>
Since Lilly started with $750 and now has $1070, the amount her mother gave her was $1070-$750 = $320.