Question 170741
OK, first take a deep breath. 
Let's get started.
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Name your variables.
G-weight of a goblet
C-weight of a cup
P-weight of a plate
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Next, write down what you know, in mathematical terms.
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"Two plates and a cup together weigh more than three goblets"
1.{{{2*P+C>3G}}}
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"Two goblets and a cup weigh more than two plates"
2.{{{2*G+C>2P}}}
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From 1,
1.{{{2*P+C>3G}}}
{{{2*P>3G-C}}}
Let's substitute that into equation 2,
2.{{{2*G+C>2P}}}
Now add what we learned above,
{{{2*G+C>2P>3G-C}}}
and remove the 2P from the middle,
{{{2*G+C>3G-C}}}
Add C to both sides and subtract 2G fom both sides,
{{{2C>G}}}
or
{{{G<2C}}}
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A goblet weighs less than two cups.