Home >> Civicrm >> Administrator civicrm >> Price Set
Create Price set With name ****
Create Price Field with Following sequence..
Input Field Type is Radio with two options
Radio one 100
Radio two 200
Second Field in same price set group
Input Field Type is Checkbox with two options
CheckBox one 50
CheckBox two 150
Now select this price set in online event registration
In Registration select value from Radio Field '$100'
and from checkbox Field '$50'
On confirmation page you see total value is $250 instead of $150