Consider the sample data for plants A, B, C & D of the above company, which are tabulated in table 1. Test whether the four means are equal at the 5% level of significance. Perform a test that will compare all 4 means at once. We are not interested in pair-wise comparisons at this stage. Please show all the steps in your calculations.

Table 1
plant A plant B plant C plant D
333 328 320 333
332 329 321 321
320 323 322 329
326 327 325 330
328 330 326 328
325 331 328 325
323 332 329 333
321 320 330 331
334 324 331 327
322 323 332
320 334
329
330
328
331
330