Answer:
The value of f is 5
Step-by-step explanation:
Initially, the number of frog tadpoles = f
The initial probability of catching a frog tadpole = f/20
Adding 10 more frog tadpoles,
Number of frog Tadpoles = f +10
Total number of tadpoles in the pond = 20+10 = 30
new probability of catching a frog tadpole = (f+10)/30
New probability of catching a frog tadpole = 2 x Initial probability of catching a frog tadpole
(f+10)/30 = 2 x (f/20)
(f+10)/30 = f/10
f+10 = f x 30/10
f+10 = 3f
2f = 10
f = 5
