Mid-caps gained on Wednesday, championed by strong performances in the construction, telecommunications and property sectors.As of 15:00 BST, the FTSE 250 was trading 1.2% higher at 17,740.Outsourcer Serco topped the risers, after first-half profits came in better than expected, although management has not altered its expectations for the full year.Pub group Greene King edged higher as it reported record retail revenue of £1bn in its full-year results, although profits leaked lower as a result of a decline in like-for-like sales and the impact of the disposal of 275 pubs to Hawthorn Leisure.Tullow Oil gained after taking action to "re-set" the business for the new oil price environment. The company also slightly increased its guidance for full-year production after enjoying strong West Africa oil production in the first half.Property stocks Redrow and Bovis Homes were on the up, while miners Lonmin, Vedanta Resources and Acacia Mining extended losses for the third consecutive day, as both base and precious metal prices fell. Analysts expressed concerns over the direction aluminium prices were headed in.Premier Oil tracked tumbling oil prices, with both benchmarks more than 1% weaker.RisersSerco Group (SRP) 126.90p +7.54%Just Eat (JE.) 433.80p +6.64%Aveva Group (AVV) 1,900.00p +5.09%Betfair Group (BET) 2,496.00p +3.74%Bovis Homes Group (BVS) 1,153.00p +3.59%Redrow (RDW) 458.30p +3.48%Balfour Beatty (BBY) 249.80p +3.27%DCC (DCC) 5,160.00p +3.20%UDG Healthcare Public Limited Company (UDG) 505.00p +3.19%Smith (DS) (SMDS) 397.70p +3.03%FallersLonmin (LMI) 107.90p -3.57%Acacia Mining (ACA) 291.80p -3.35%Nostrum Oil & Gas (NOG) 578.00p -2.45%Telecom Plus (TEP) 970.50p -1.97%AO World (AO.) 142.00p -1.87%IP Group (IPO) 203.50p -1.45%Euromoney Institutional Investor (ERM) 1,200.00p -1.40%Computacenter (CCC) 766.00p -1.29%Kaz Minerals (KAZ) 200.80p -1.28%Vedanta Resources (VED) 513.50p -1.25%