Sloanne bought 20 erasers and pens in total. Each pen costs $2 while each eraser costs $0.50. If he spent $32.50 in all, how many erasers did he buy?

We can make a system of equations:

x + y = 20

2x + 0.50y = 32.50

Where 'x' is the number of pens and 'y' is the number of erasers.

x + y = 20

x = - y + 20

Plug in - y + 20 for 'x' in the 2nd equation:

2 (-y + 20) + 0.50y = 32.50

Distribute 2:

-2y + 40 + 0.50y = 32.50

Combine like terms:

-1.5y + 40 = 32.50

Subtract 40 to both sides:

-1.5y = - 7.5

Divide - 1.5 to both sides:

y = 5

Plug this into any of the two equations to find 'x':

x + y = 20

x + 5 = 20

Subtract 5 to both sides:

x = 15

So he bought 15 pens and 5 erasers.

Answer: 15 pens and 5 erasers

15*$2=$30 & 5*$.50=$2.50

$30+$2.50=$32.50