Mary Jo spends $1,450 to buy stock in two companies. She pays $15 a share to one of the companies and $20 a share to the other. If she ends up with a total of 90 shares, how many shares did she buy at $15 a share and how
many did she buy at $20 a share?

she bought 70 shares of the $15 shares

she bought 20 shares of the $20 shares

Step-by-step explanation:

this would be solved using simultaneous equation

let a = $15 shares

b = 20 shares

a + b = 90   equation 1

15a + 20b = 1450  equation 2

Multiply  equation 1  by 15

15a + 15b = 1350  equation 3

subtract  equation 3 from  equation 2

5b = 100

b = 20

substitute for b in  equation 1

20 + a = 90

a = 70