They contain a range of different products, which are sold at a lower price than their combined value.

它们包含一系列不同的产品，售价低于这些产品的总价值。

" To be on sale" (sale) means it is being sold at a lower price than usual, than normal.

“To be on sale” (sale) 表示它正在以比平时更低的价格出售， 比正常情况要低。

So, if you undercut your competitors, you sell what you are selling at a lower or much lower price.

所以， 如果你以低于竞争对手的价格出售，你就会以更低或更低的价格出售你所销售的产品。

Paresh's mother also " stocked up when things were on sale" – that is, when they were being sold at a lower price by the store.

Paresh 的母亲还“在打折时囤货” ——也就是说，当它们被商店以较低的价格出售时。