00:01
So here we're asked to find an elasticity.
00:03
Remember, elasticity is the percentage change in quantity over the percentage change in price.
00:09
We know that the quantity is going from 20 to 10.
00:12
We know that the price is going from 4 to 5.
00:17
And we know that a percentage change is equal to the new minus the old over the old.
00:24
Right? that's the definition.
00:26
So all we need to do here is to plug things in.
00:28
Quantity, the new quantity is 10, the old is 20, the old was 20.
00:36
The price is 5, was 4, was 4, so this is equal to minus a half over a quarter, which is equal to minus 2, right? notice that there is a negative sign because we're thinking about a demand curve, right? right, a demand curve slopes down.
00:57
If price goes up, the quantity should go down...