Combining two inputs, where the group take up all width (100%), and the size is not 50% - 50%, no additional css. I made it nicely by the following code:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>_x000D_
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>_x000D_
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"/>_x000D_
_x000D_
<div class="container">_x000D_
<form>_x000D_
<div class="form-group">_x000D_
<label>Name</label>_x000D_
<div class="input-group" style="width:100%">_x000D_
<span class="input-group-btn" style="width:100px;">_x000D_
<select class="form-control">_x000D_
<option>Mr.</option>_x000D_
<option>Mrs.</option>_x000D_
<option>Dr</option>_x000D_
</select>_x000D_
</span>_x000D_
<input class="form-control" id="name" name="name" placeholder="Type your name" type="text">_x000D_
</div>_x000D_
</div>_x000D_
</form>_x000D_
</div>
_x000D_