Evaluating an expression means either to solve the expressions or to simply it.
Solving an expression:
2 - (10 + 5)
A simply expression. After doing the math the answer comes out as -3.
2x + 3x
This is an algebraic expression. This means we have variables like x and y.
In this case, we can only simplify it. Because we don't know what x is equal to.
Because they are like terms (which means they have the variable) we can add them to together.
2x + 3x = 5x
I hope this answer clears up any misunderstandings about expressions and over all helped you learn something! If you still need some help, don't hesitate to DM on Brainly! I wish you best of luck on your journey of math!
EDIT:
Now what if you have an expression like this:
5x + 5m where x=4 and m=8
In mathematics, something like 5x is the same difference as 5 * x.
And x is just a placeholder for a number or for another variable.
And in this equation, x is equal to 4. So, we just replace x with 4.
5(4) + 5m
Same this with m. The variable m is equal to 8.
5(4) + 5(8)
We can solve!
5(4) + 5(8) = 20 + 40 = 60
Our answer is 60.
Cobalt has an atomic number (Z) of 27, which means the nuclei of all its isotopes have 27 protons. Cobalt 60 has an atomic mass of 60, so it has 60-27 = 33 neutrons.
The mass of 27 isolated protons plus the mass of 33 isolated neutrons would be:
27*(1.007825 u) + 33*(1.008665 u) = 60.497220 u
The actual mass of the nucleus of 60-Co is 59.933820 u.
Mass defect: 60.497220 u - 59.933820 u = 0.563400 u
The mass defect is equal to the binding energy of a nucleus.
using the fact that 1 u = 931.5 MeV/c^2
(0.563400 u)*(931.5 MeV/u) = 524.807 MeV
1.323 as a percent is 132.3% because you take the decimal and move it two spaces to the right->
