Pete is having a cup of black coffee with breakfast. The glass weighs 100g and holds 100mL, so he says that the drink (the cup and coffee together) weighs 200g. Explain why Pete is mistaken

The units g and mL measure different quantities.

Step-by-step explanation:

Pete knows the glass weighs 100g, so this is the weight of the cup.

It holds 100 mL, however, mL measures volume, not weight.

Pete is wrong about saying that the cup and coffee together weigh 200 g, because you cannot add two values together that have different units.

In this example, you cannot add together the weight of the cup and volume of the coffee, in order to get the total weight. You would have to find the weight of the coffee, then add that to the cup's weight.

So, Pete is wrong because you cannot add 2 values together that have different units.

-2 is the right