To begin, let's find how much the book is including tax and the student discount. Once we find this, we can see if Lara or Alex is correct and if they can afford it.
First, we want to compute the student discount. The student discount is 35%. Thus, we can do 0.65 x 28.50 = 18.525. With 10% tax, we have 18.525 x 1.1 = 20.3775. Which will round up to $20.38.
Now, lets see what Alex did and if he got the same answer. First he takes 35% of $28.50 and subtracts it from the normal price.
.35 x 28.50 = 9.975
28.50 - 9.975 = 18.525
Then he takes 10% of this number and adds it back.
.10 x 18.525 = 1.8525
18.525 + 1.8525 = 20.3775
Alex has the correct answer.
Next, we will see if Lara computed it correctly.
First she takes 65% of the normal price.
0.65 x 28.50 = 18.525
Then she computes 110% of the reduced price.
18.525 x 1.10 = 20.3775
Lara also gets the correct answer.
So, do they have enough money to purchase the book?
YES:
$20.38 < $21
Is Alex correct?
YES
Is Lara correct?
YES
Although they used different methods to get the answer, they both got the right one!