A container contains red and blue marbles. Exactly 20% are red. After adding 10 red marbles, the container is now 36% red marbles. How many total marbles were in the container initially?
40
Let original total be T. Original red = 0.2T. After addition: (0.2T + 10) / (T + 10) = 0.36. 0.2T + 10 = 0.36T + 3.6 => 6.4 = 0.16T => T = 40.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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