a formula that can be used for this circumstance is a linear y=mx+b problem. for 1 salamander there are 10 frogs. so with this we can state that y=10x. whatever you plug into the x for the number of salamanders will give you the answer of how many frogs are in the pond. for example.
Y=10x
Y=10(3)
Y=30
30 frogs.
also because 10 is a nice number you can just multiply the number of salamanders times 10. 3*10=30