Freya’s mother, Ingrid, was a mountain rescuer, and her partner was a big, fluffy dog called Tundra. Tundra’s job was to find people who were lost or hurt on the snowy slopes. With her powerful nose, she could smell a person even under the snow.

One winter weekend, Freya stayed with her mother at the rescue hut high in the mountains. Freya loved the hut, with its warm stove and its maps on every wall. But she did not like the big radio on the desk. When it crackled, her stomach twisted. Talking to strangers, even on a radio, made her feel anxious.

That afternoon, a call came in. A skier had fallen near the frozen lake and could not walk. Ingrid clipped on Tundra’s orange vest. “Stay by the radio, Freya,” she said. “If the helicopter calls, tell them where we are.” Then they disappeared into the white hills.

Freya waited. The clock ticked. Suddenly the radio crackled. “Rescue hut, this is the helicopter. Where is the team?” Freya’s hands shook. She wanted to hide under the desk. Then she remembered how Tundra always kept going, even in deep snow.

Freya picked up the radio and pressed the button. “This is the rescue hut,” she said. Her voice wobbled at first. “The team is at the frozen lake, on the north side.” She looked at the map and added, “Next to the three tall rocks.”

“Thank you, rescue hut. Great job,” said the pilot.

That evening, the skier was safe in hospital with a broken ankle. Tundra was snoring by the stove. Ingrid hugged Freya tightly. “You helped save someone today,” she said. Freya smiled. Next time the radio crackled, she thought, she might even be the first to answer.

Every class at Hana’s school in Osaka, Japan, looked after a small vegetable garden. Hana’s class grew tomatoes, cucumbers and sweet potatoes. But there was a problem: the summer holidays were coming, and for two weeks nobody would be at school to water the plants.

“The tomatoes will dry up,” said Hana’s friend Kenji gloomily. “All our work will be wasted.”

Their teacher, Ms Mori, smiled. “Then let’s think like engineers. What do plants need, and how can we give it to them while we are away?”

The class had lots of ideas. Someone suggested asking the school caretaker, but he was going on holiday too. Someone else suggested a giant umbrella to keep the sun off, but plants need sunlight to grow.

Hana thought about the empty plastic bottles in the recycling bin. “What if each plant had its own water bottle?” she said. “If we make a tiny hole in the lid and push the bottle upside down into the soil, the water will drip out very slowly.”

Kenji’s face brightened. “But if the hole is too big, the water will all run out in one day. We need to test it!”

For the next week, the class experimented. They made holes with a thick nail, a thin nail and a pin. They timed how long each bottle took to empty. The pin hole was too slow, and the thick nail hole was far too fast. The thin nail hole was just right: a big bottle lasted about four days.

“So each plant needs two bottles to last a week,” said Kenji, doing the maths. The families agreed to take turns visiting once a week to refill them.

When school started again, the tomatoes were red and ripe, and the cucumbers were longer than Kenji’s hand. Ms Mori pinned a sign on the garden gate: “Designed by the Class 4 Engineers”.