• Select the shapes you want to merge by holding down the Shift key while selecting each one individually.
• Select Merge Shapes from the Insert Shapes group on the Drawing Tools Format tab, and then choose the option you desire.
• (If no shapes are selected , the Merge Shapes button will be greyed out.)
• The effect of each of the Merge Shapes options is seen in the second image above.
• The options displayed to you may be affected by the sequence in which you select the shapes to merge. If you're not happy with the results, start over by unselecting the shapes, and then repeat the process, this time selecting a different shape than you did the first time.
  

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