Answer:
Let x be the number of shares bought at $1.75 per share and y be the number of shares bought at $3.25 per share. Then we have the following system of equations:
x + y = 400 (the total number of shares is 400)
1.75x + 3.25y = 1112.50 (the total cost of the shares is $1112.50)
We can solve for x by rearranging the first equation:
x = 400 - y
Substituting this into the second equation, we get:
1.75(400 - y) + 3.25y = 1112.50
Expanding and simplifying, we get:
700 - 1.75y + 3.25y = 1112.50
1.5y = 412.50
y = 275
Substituting this value of y back into the equation x + y = 400, we get:
x + 275 = 400
x = 125
Therefore, the investor bought 125 shares at $1.75 per share and 275 shares at $3.25 per share.