Answer: $23.80
Explanation:
To solve this problem, we can set up a system of equations based on the given information.
Let's assume the price of one composition book is "x" dollars and the price of one pen is "y" dollars.
From the first sentence, we know that:
7x + 4y = 30.20 (Equation 1)
From the second sentence, we know that:
2x + 21y = 40.40 (Equation 2)
To solve this system of equations, we can use either substitution or elimination method. Let's use the elimination method here:
Multiply Equation 1 by 2 and Equation 2 by 7 to eliminate the "x" term:
14x + 8y = 60.40 (Equation 3)
14x + 147y = 282.80 (Equation 4)
Now, subtract Equation 3 from Equation 4 to eliminate the "x" term:
(14x + 147y) - (14x + 8y) = 282.80 - 60.40
14x - 14x + 147y - 8y = 222.40
139y = 222.40
Divide both sides by 139:
y = 222.40 / 139
y ≈ 1.60
Now, substitute the value of y back into Equation 1:
7x + 4(1.60) = 30.20
7x + 6.40 = 30.20
7x = 30.20 - 6.40
7x = 23.80