Turn $20\%$ into a decimal. What number should you multiply $50$ by to find $20\%$ of it?

You can either find $20\%$ of $50$ and subtract that from $50$, or directly find $80\%$ of $50$ (because that's the portion you still pay).

After you find the discount amount or the remaining percentage, do the final multiplication or subtraction carefully to avoid a simple arithmetic mistake.

In Desmos, type either 50*(1-0.20) or 50*0.80 and look at the output. The value Desmos gives is the sale price after a 20% discount is applied to $50.

A 20% discount means the price is lowered by 20% of the original price. So you either:

• Find 20% of $50$ and subtract that from $50$, or
• Pay the remaining $100\%-20\%=80\%$ of the original price.

Convert $20\%$ and $80\%$ to decimals:

• $20\%=0.20$
• $80\%=0.80$ You can use either one depending on which method you choose.

If you choose the "subtract the discount" method:

• Calculate $20\%$ of $50$:
  $0.20 \times 50 = 10$
  This tells you the discount is $10, which you will subtract from the original price.

Now subtract the discount from the original price:

• Original price: $50
• Discount: $10
• Sale price: $50 - $10 = $40

So, the sale price of the backpack is $40.