Solve These Sample Mysteries!

From One Minute Mysteries:
65 MORE Short Mysteries You Solve With Science!

1. Tanks A Lot

When Giselle and Camilla finally got the aquarium they had wanted in their room, their mother reminded them that they had promised to take good care of the fish.

“You need to replace a third of the water every week,” she said as they set up the tank. “And once a month, put the fish in another container, clean everything and put in all new water.”

“That sounds like two equal jobs,” Giselle said when the girls were alone later. “One person changes a third of the water every week and the other does the complete change once a month. Doesn’t matter to me. Take your pick.”

“I’ll change a third of the water every week,” Camilla said.

“Deal,” Giselle said.

“And I’ll do it the easy way,” Camilla added.

“What do you mean?” Giselle asked.

“I won’t have to take out old water,” Camilla said. “I’ll just leave the top off the tank. Over a week, about that much will evaporate. Then all I’ll need to do is put in the fresh water.”

“That’s not fair!” Giselle said.

“Sorry, we had a deal,” Camilla said.

“I mean it’s not fair to the fish,” Giselle said.

“What do you mean, not fair to the fish?” Camilla asked.

Answer for Tanks A Lot

2. Time for a Change

Ivan’s father had bought new smoke detectors six months earlier, putting one on each level of their house: one in the laundry room downstairs, one in the sunroom on the main level and one in the upstairs hall between the bedrooms. The smoke detectors sent wireless signals to an alarm system.

Ivan’s father had asked him to replace the batteries and looked surprised when Ivan brought the smoke detectors to him where he was working at his tool bench in the garage. That was where they kept the fresh batteries.

“You didn’t have to take them off their bases,” his father said. “You could have just taken the new batteries, opened each smoke detector where it was, and switched the batteries there.”

“Sorry, I guess I didn’t understand what you meant,” Ivan said. “Can’t we just change them here?”

“We’ll do that, but we have to put each smoke detector back in the same place or the alarm system won’t work right,” his father said. “And they’re all the same, except that the color of one is more faded than the others and one has some dark spots.”

“At least that tells us what we need to know, doesn’t it?” Ivan asked.

Answer for Time for a Change

3. Eggcellent Idea

“Mom, where are you?” Carol called as she unlocked the back door and entered the kitchen.

Three other equally sweaty and hungry girls followed her after playing a pick-up soccer game on the field near Carol’s house. On the table, they saw a note from Carol’s mother.

It said, “Had to run an errand. Will be back around one. You and your friends can help yourself to lunch. Eggs are in the fridge.”

“Mom boiled a dozen eggs this morning to make egg salad sandwiches. I know how to make them,” Carol said as she opened the refrigerator.

Two identical egg cartons were inside.

“How do we know which dozen is hard-boiled?” Bianca asked. “If we crack one open and it’s still raw, we’re wasting an egg and making a mess.”

“How about seeing if any are still warm?” Jade suggested. “Or still wet from being in the water?”

Carol brought out both egg containers and felt the eggs. All the eggs were cold and dry.

“That doesn’t help. They’re all the same. I think we have to guess,” she said.

“We don’t have to guess,” Lucy said.

All their heads turned toward her.

Answer for Eggcellent Idea

Answers to these Mysteries

1. Tanks A Lot

“The point of changing water is that you’re taking out some of the old water that has gotten dirty from uneaten food and from the fish living in the water,” Giselle said.

“If you just let water evaporate, the dirty stuff stays in the water left behind and it’s even worse for the fish because it’s more concentrated.”

“Okay, I’ll take out old water,” Camilla said. “We’ve been asking for these fish for a long time and we should take care of them the right way.”

2. Time for a Change

“This faded one must be the one from the sunroom, the brightest of the three places,” Ivan said, setting aside the one with the lighter color. “And the dark spots on this one are mildew, meaning it must have come from a damp, dark place—the laundry room. That leaves the other one for the upstairs hall.”

3. Eggcellent Idea

Lucy explained, “Spin the eggs here on the counter. They will spin differently. The raw ones will spin more slowly than hard-boiled ones. That’s because the hard-boiled eggs have been cooked solid, but the liquid inside of the raw egg will slow the egg down. That’s how we will be able to tell which eggs are which.”