This circuit can NOT be reduced using basic series and parallel reductions. Instead this problem must be solved using loop rule and junction rules.
The physics of this problem is not overly difficult, however the algebra causes most people to get lost in solving the problem. Here we take a look at using Ohm's Law to set up a system of equations that can be used to solve for the current and voltage at each resistor as well as the equivalent resistance of the entire circuit.
Yes you can use a Delta-Y transformation here, but often people encounter this problem before learning that technique.
The topic of Wheatstone Bridges often comes up in introductory physics and engineering courses such as AP Physics C E&M, Electricity and Magnetism, Physics 202, Physics 8.02 and appears on A Level physics as well as the JEE.