When something increases threefold (3 times) is that 300% on the initial number?

Yes

Step-by-step explanation:

300% when converted to a fraction is 3/1 which is 3. hence, you are correct to say that

You can have a look on the ways to convert between fractions and percentage on my Instagram (learntionary) if you are interested. I do post other good tips for math there too thanks!

twenty-six miles over two gallons because the proportion for the original 13 miles to one gallon would be written 13/1 and, doing the same thing to the top and bottom, i multiplied by 2 and got 26/2

the forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?