Natural numbers are closed under division: false.
A set is closed under a certain operation if the results of that operation are always inside that set.
So, if natural numbers were closed under division, the division of two natural numbers would always be a natural number.
You have plenty of counterexamples, to pick one you may divide any odd number by 2: 5/2 is not a natural number.
Negative numbers are closed under addition: true.
Let 
be two positive numbers. So, 
are two negative numbers. Their sum is
And since 
is positive, we deduce that 
is negative, so the sum of two negative numbers is still negative.
Prime numbers are closed under subtraction: false.
This would mean that the subtraction of two primes is also a prime. Again, there are many counterexamples: 7 is prime and so is 3, but their difference 7-3 is 4, which is not prime.
Answer:
7161 km³
Step-by-step explanation:
28²+b²=32.5²
784+b²=1056.25
b²=1056.25-784
b²=272.25
b=√272.25
b=16.5
1/2x28x16.5x31=7161
Answer:
months
For x = 9, the number of months will be 96.83.
Step-by-step explanation:
Linda’s savings account has fallen below the $1,000 minimum balance required to receive interest. It is currently $871.43. The monthly fee charged by the bank for falling below the minimum is x dollars.
Now, the number of months it will take Linda's account to reach a zero balance will be given by
months. (Answer)
Now, if x = 9, then 
months. (Answer)
Answer: C- 4,3 D- 9,4 E- 4,5 F- 1,4
Step-by-step explanation:
