There were 350 goldfish and guppies in a shop. 20% of them were goldfish. After some goldfish were added, the percentage of goldfish increased to 30%. How many goldfish were added?

Answer 1

First, we need to figure out how many goldfish and guppies there were originally.

We know that 20% of the total were goldfish, so we can set up an equation:

0.2(Total) = 350

Solving for the total:

Total = 350 / 0.2

Total = 1750

So there were originally 1750 fish in total, and 20% of them were goldfish, which means:

Goldfish = 0.2(1750)

Goldfish = 350

Now we need to figure out how many goldfish were added to increase the percentage to 30%. Let's call the number of goldfish added "x".

We know that the new percentage of goldfish is 30%, so:

(Goldfish + x) / (Total + x) = 0.3

Substituting in what we know:

(350 + x) / (1750 + x) = 0.3

Multiplying both sides by (1750 + x):

350 + x = 0.3(1750 + x)

Distributing on the right side:

350 + x = 525 + 0.3x

Subtracting 0.3x and 350 from both sides:

0.7x = 175

Dividing both sides by 0.7:

x = 250

So 250 goldfish were added to the shop.