Final answer:
To calculate the discount with the voucher, we need to find 20% of the total cost and subtract it. The voucher will provide a $40 discount on the total cost of two items.
Step-by-step explanation:
The subject of this question is Mathematics, and it is at a High School level.
To solve this problem, we need to calculate 20% of the total cost and subtract it from the original cost. For example, if the original cost is $100, 20% of $100 is 0.20 x $100 = $20. So, the voucher will reduce the cost by $20. If Jack is buying two items with the voucher, the total discount will be $20 x 2 = $40.
Therefore, Jack will get a $40 discount on the total cost of the two items with the voucher.