Help plzzzzzz?

 1).
 400 as a product of its primes:
 400 = 2^4 × 5^2 
 2). 
 205 as a product of its primes:
 205 = 5 × 41 
 3). 
 7/14 reduced to the lowest terms:
 1/2 
 4). 
 3/7 of 42 = 18 
 5). 
 The National Safe Kids Campaign and Bell Sports sponsored a study 
 that surveyed 8,159 children ages 5 to 14, who were riding bicycles.  
 Approximately 2/5 of the children were wearing helmets and of those,  
 only 13/20 were wearing helmets correctly.  
 8,159 × (2/5) × (13/20) = 2121.34 
 About 2121 of the children were wearing helmets correctly....Show more

Keep dividing by primes until the result is 1
400/2 = 200
200/2 = 100
100/2 = 50
50/2 = 25
25 /5 = 5
5/5 = 1

prime factors
400 = 2 * 2 * 2 * 2 * 5 * 5
400 = 2⁴  * 5²  <–––––...Show more