Final answer:
The amount paid for shirts varies directly with the number of shirts, confirming the statement as true. If a t-shirt is sold for a certain price, the total cost is the price per shirt multiplied by the number of shirts, illustrating direct variation.
Step-by-step explanation:
The statement 'The amount paid (a) for the purchase of shirts varies directly with the number (n) of shirts bought' is true. This is because in direct variation, when one quantity increases, the other quantity increases at a constant rate. This can be expressed in the form a = kn, where k is the constant of variation which, in this case, represents the price per shirt.
For instance, if Coolshirts sells a t-shirt at a price of $9 each, purchasing 10 t-shirts would cost $90. Here, the total cost is directly proportional to the number of t-shirts. If you bought 5 t-shirts instead, at the same price, you would pay $45, again showing a direct correlation between the number of shirts and the total cost.