Four electric resistance furnaces are tested to determine the temperature produced in each one.

The four furnaces differ only in the composition of the coil of wire that is wound on the refractory material. A number of measurements of temperature (°C) are made for each furnace and are given below. Use a 5% level of significance in determining whether or not the mean temperatures produced in the furnaces differ. If an overall difference is found, determine the furnace or furnaces that differ significantly.

Furnace 1 1250 1175 1275 1200 Furnace 2 1400 1375 1525 1475 Furnace 3 1350 1375 1325 1425 Furnace 4 1625 1575 1650 1675