Discuss and Choose

This activity challenges you to decide on the 'best' number to use in each of the following statements.
 
You may like to talk to someone else about what you're thinking.  You may need to do some estimating, some calculating and some research.
 
Please send us your solutions and don't forget to explain how you arrived at your conclusions.
 
 
 
1) There are roughly $10/500/1000$ million domestic cats in the world.
2) On average, cats weigh $1.5/4.5/8$ kg.
3) Domestic cats sleep on average $8-9/13-14/18-19$ hours a day.
 
 
4) There are roughly $400/600/800$ million domestic dogs in the world.
5) The average life of a dog is $10-14/14-18/18-20$ years.
 
 
 
6) Dolphins live in groups called pods or schools of up to $12/20/30$ individuals.
 
 
7) Adult elephants need to drink about $100/200/400$ litres of water a day.
 
 
8) A giraffe's neck is about $120/170/220$ cm long.
9) A giraffe's tail hair is $2/5/10$ times as thick as the average human hair.
 
 
10) On average, male lions weigh $180/250/330$ kg.
11) A lion's roar can be heard $8/12/16$  kms away.
12) On average, lions rest for $10/15/20$ hours a day.