A highway is being extended from its current length of 200 miles up to 650 miles. 50 miles are built on the first day, and three times this amount are built on the second day.  How many miles still need to be added to the highway to finish extending it?
The length of the highway that needs to be constructed is 650 – 200 = <<650-200=450>>450 miles.
After the first day, there are still 450 – 50 = <<450-50=400>>400 miles that need to be constructed.
On the second day, 50 miles * 3 = <<50*3=150>>150 miles are added to the highway.
This means that 400 – 150 = <<400-150=250>>250 miles still need to be added to the highway.
#### 250