To find the number of pens and notebooks Gabriel bought, let's use a system of equations.
Let's assume Gabriel bought x pens and y notebooks.
According to the problem, pens cost $1.50 each and notebooks cost $3.00 each. Therefore, the total cost can be calculated as follows:
Total cost = (Cost of pens * Number of pens) + (Cost of notebooks * Number of notebooks)
30 = (1.50 * x) + (3.00 * y)
The problem also states that Gabriel bought a total of 15 items. So, the total number of items can be expressed as:
Total items = Number of pens + Number of notebooks
15 = x + y
We now have a system of equations:
1.50x + 3.00y = 30
x + y = 15
To solve this system of equations, we can use substitution or elimination. Let's use the elimination method.
Multiply the second equation by 1.50 to make the coefficients of x in both equations the same:
1.50(x + y) = 1.50(15)
1.50x + 1.50y = 22.50
Now, subtract the first equation from the modified second equation:
(1.50x + 1.50y) - (1.50x + 3.00y) = 22.50 - 30
-1.50y = -7.50
y = -7.50 / -1.50
y = 5
Substitute the value of y into the second equation:
x + 5 = 15
x = 15 - 5
x = 10
Therefore, Gabriel bought 10 pens and 5 notebooks.