At a local zoo, the number of resident birds is twice the number of four-legged mammals. If the total number of legs between the birds and mammals equals 80, how many birds are there?

Step-by-step explanation:

Total number of legs = 80

So if there are 10 mammals so there legs = 40

And the no of resident birds should be twice

So there are 20 resident birds and number of legs = 20 * 2 = 40