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Jane had several stamps. She gave 10 of them to her friend. Afterwards, Jane’s mom bought her twice as many stamps as she had in the beginning. How many stamps did Jane have in the beginning if she now has a total of 50 stamps?

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AlpenGlow
The answer is 20 stamps. 

You can solve this by forming an equation with. 

We know that she has a total of 50 at the end. So we will put the 50 stamps at the end of the equation and derive for the unknown. 

She first gave 10 to her friend. This means we subtract first 10 from the unknown. Let x represent the unknown. 

x-10

Afterwards Jane's mom bought her twice as many as she had at the beginning. So we know that we add twice as much as the unknown. 

x-10+2x = 50

Now we solve. Let's arrange our terms by combining like terms:
3x - 10 = 50

Now we transpose the 10 to the other side of the equation:
3x = 50 + 10
3x = 60

And finally we transpose the 3 by the x to isolate x:
x = 60/3
   = 20 

She had 20 stamps in the beginning.

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