Page 130 - NUMINO Challenge_A2

2 Since the magic flowers covered half of the surface of the water on the 9th day, twice as
many flowers are needed to cover the surface completely.

3 When the number of magic flowers is doubled on the first day, the surface area that the
flowers cover on days 2, 3, ,9 doubles everyday as well. Therefore, to completely cover
the surface of the water in the fishbowl on the 9th day, Lisa needs to put in 2 magic
flowers on the first day.

Problem solving

1 Day Time Night Time
8m 8 4 4m
1st Day 12 4 8 m
2nd Day 4 8 12 m 16 4 12 m
3rd Day 8 8 16 m 20 4 16 m
4th Day 12 8 20 m
5th Day 16 8 24 m

Therefore, the snail will get out of the well during the day on the 5th day.

2 In order for 2 germs to fill a bottle, 1 germ must fill half the bottle. Since the number of

germs doubles every hour, and 1 germ can fill the bottle in 8 hours, the bottle will be half

filled within 7 hours. Therefore, it will take 7 hours for 2 germs to fill the bottle.

25Answer Key