It is given that triangle FED is similar to tri STU. Is it true to say that DE/ST =FE/TU. If not why

Answer : 

If $∆$ FED $~$ $∆$ STU  ,
So we know corresponding sides are in proportion , So the ration of sides  



$\frac{DE}{UT} = \frac{FE}{ST}$ 

SO the given ratio is wrong , Because $\frac{DE}{ST} = \frac{FE}{TU}$   is not the ratio of the corresponding sides  .