This apparent contradiction of the timing of the events involved Jesus’ cleansing the Temple and cursing the fig tree. Matthew 21:12–19 reports that Jesus cursed the fig tree on the day following His cleansing of the Temple. However, Mark 11:12–24 appears to indicate that Jesus left Bethany (v. 12), cursed the fig tree for not having fruit (v. 14), then He arrived in Jerusalem (v. 15) and cleansed the Temple. Then Jesus and His disciples left Jerusalem that evening to return to Bethany (vv. 19–20). The next morning (the morning after Jesus had cursed the fig tree) they saw that same fig tree withered.
According to Mark’s reporting, the disciples saw the fig tree withered upon Jesus’ second trip to the Temple. Matthew does not describe two separate trips to the Temple—he combines them into what seems one entry into the Temple to cast out the money changers. Craig Blomberg explains Matthew’s intent:
Mark notes that a night intervenes before this next event (Mark 11:11–12), but Matthew characteristically abbreviates his narrative and omits this notice. Jesus’ whole purpose in entering Jerusalem is to go to the temple, so Matthew takes his readers straight there.
In this way the discrepancy is resolved.
 Craig Blomberg, Matthew, New American Commentary 22 (Nashville, TN: Broadman & Holman Publishers, 1992), 314. Also, Michael P. Green, The Message of Matthew: The Kingdom of Heaven, The Bible Speaks Today (Downers Grove, IL: InterVarsity Press, 2001); 222–23.