The number of goldfish Ben has is unknown, so we'll call that number x. If he had 3 times as many guppies as goldfish, then the number of guppies he has is 3x. The number of fish he has in all, 20, is the number of guppies + the number of goldfish. guppies + goldfish = 20. The number of goldfish is x and the number of guppies is 3x, so guppies + goldfish is:
x + 3x = 20. Now, add the x's:
4x = 20. Now, divide both sides by 4 (always do the same thing to both sides of the equation to keep them the same).
4x/4 = 20/4. 4/4 = 1, so
1x = 20/4
x = 5. This is the number of goldfish he has. To find out the number of guppies he has, subtract this number from the total number of fish:
20 - 5 = 15. Therefore, he has 15 guppies.Since 15 = 3 x 5 and Ben has 3 times as many guppies as goldfish, both of these numbers are correct: 5 goldfish and 15 guppies.:-)
