Answer:
[tex]\text{ 21 combinations}[/tex]
Explanation:
Here, we want to get the total number of possible combinations
There are a total of 7 buttons
The first has 6 options
The second has 5 options
The third has 4 options
The fourth has 3 options
The fifth has 2 options
The sixth has 1 option
The seventh has 0 options (it would have been pressed at same time with other buttons already)
Thus, the total number of possible combinations will be:
[tex]6+5+4+3+2+1\text{ = 21 combinations}[/tex]
