Answer: 115 gold memberships were sold that day.
Explanation:
Let x represent the number of silver memberships that were sold that day.
Let y represent the number of gold memberships that were sold that day.
The website sold a total of 307 memberships in one day. This is expressed as
x + y = 307
The silver membership costs 5.00 and the gold membership costs 7.50. The website earns 1822.50 that day for selling both memberships. This is expressed as
5x + 7.5y = 1822.5- - - - - - - - - - -1
Substituting x = 307 - y into equation 1, it becomes
5(307 - y) + 7.5y = 1822.5
1535 - 5y + 7.5y = 1822.5
- 5y + 7.5y = 1822.5 - 1535
2.5y = 287.5
y = 287.5/2.5
y = 115
x = 307 - y = 307 - 115
x = 192