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Hi! I'm Sean with Expert Village and I'm going to show you tips and tricks for doing math
in your head. We already learned how to multiply with 9s, but what if we wanted to multiply
with 99. There's a very similar trick we can use when we remember that 99 is the same as
100-1. Let's take 99x43 as our example. We can express this as (100-1)x43. If we multiply
this out, we'll get 4300-43. To simplify it even further, we can round that 43 up to 50.
4300-50 will give us 4250. Since we subtracted an extra 7 to round it up to 50, we want to
add that 7 back. 4250+7 will equal 4257, which is our answer. Whenever you're doing math
in your head, the most important part is being able to visualize the numbers. The more you
practice, the better you're going to get.