Identifying incorrect circle measurements

0:00- [Instructor] We're told that Liam measured the diameter and circumference of four circular objects at home. He made an error when measuring one of the objects. Which object did Liam measure incorrectly? Pause this video and have a go at that. Alright, so the key clue here is that these are four circular objects and you might already know that the ratio between the diameter of a circle and the circumference, or I should say the circumference and the diameter, this is hand drawn, sorry, not the perfect circle.

0:33So this is the circumference and that this is the diameter right over here, that the ratio circumference divided by diameter, is always going to be the same. It's a special number, 3.14159, and it keeps going on and on and on, which we call Pi. So if we look over here, let's see if all of them, roughly it might not be perfect 'cause he's taking measurements in the real world.

0:58So it might not be always exactly this, but let's see if it's roughly that. When I go from the diameter to the circumference here, it looks like I am multiplying by three point something. If I multiply 26 times three, that would get me to 78. So this does look like three point something something, seven times, three point something something also would get us to 22 point something.

1:25So that seems reasonable. If I took nine times, three point something, something, that would be 27, 28, depending on how much we multiply. But that looks pretty close. Now eight times three point something, something would get us over 24, but this is 20, so this is pretty far from something that is over 24, maybe even 25.

1:49So this is the one, this is the object, the duct tape roll that Liam measured incorrectly. Or maybe the duct tape roll wasn't perfectly circular. That's the other possibility here.