<PRE><B>Question 756177</B>
Robert gave one half of his marbles to Dean.
Then he gave two thirds of the remaining ones to Mark.
 If he ended up with 10, how many did he have when he started?
:
let x = original no. of marbles
Then
(.5x) = amt given to Dean
and
{{{2/3}}}(.5x) = amt given to Mark
Hence the equation
x - .5x - {{{2/3}}}(.5x) = 10
which is
.5x - {{{2/3}}}(.5x) = 10 
multiply by 3 to get rid of the denominator
1.5x - 2(.5x) = 30
1.5x - 1x = 30
.5x = 30
Multiply both sides by 2
x = 60 marbles originally
:
:
See if that works
He gave 30 to Dean and {{{2/3}}}*30 to Mark
60 - 30 - 20 = 10</PRE>