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.

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  <–––––