SOLUTION: I'm trying to help my boys with this homework and I have no idea how to do this. I don't want to just give them the answer. x+5 for x=-18 z/-6 for z=96

Question 83058This question is from textbook Holt Middle School Math Course 2
: I'm trying to help my boys with this homework and I have no idea how to do this. I don't want to just give them the answer.
x+5 for x=-18
z/-6 for z=96 This question is from textbook Holt Middle School Math Course 2

Found 2 solutions by scott8148, bucky:
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
you substitute (plug in) the value of the variable (letter) in the expression and evaluate

x+5, x=18 ... so 18+5=23

z/-6, z=96 ... so 96/-6=-16
Answer by bucky(2189) (Show Source): You can put this solution on YOUR website!
x+5 for x=-18
.
Just substitute -18 for x and the problem becomes:
.
-18 + 5
.
When you add numbers having opposite signs the rule is subtract the two numbers and give
it the sign of the larger number. In this case subtract 5 from 18 to get 13 and give the
answer the same sign as the 18 ... which is a minus sign. Another way to look at this is
go to -18 on the number line, then count 5 units to the right (the same as adding -18 and
+5) and you end up at -13.
.
for z=96
.
Substitute 96 for z and the problem becomes:
.

.
The rule is when you divide two numbers that have different signs, the answer is negative.
So divide 6 into 96 and you get 16, but since the signs are different (the 96 is positive
and the 6 is negative) the answer is negative. So the answer is -16.
.
Here are some general rules for combining numbers (including the above rules):
.
Adding:
.
If the numbers have the same signs (both numbers are plus or both numbers are minus,
just add the numbers and give them the common sign. (Examples +6 +9 = +15 but -6 -9 = -15).
.
If the numbers being added have different signs, subtract the two numbers and give the
result the sign of the number that is the largest magnitude. See the first problem
above.
.
Subtracting:
.
Change the sign of the number being taken away and then follow the rules above for adding.
Examples:
Take -6 from +25. Change the -6 to +6 and then add it to +25 to get +31.
Take +5 from -19. Change the +5 to -5 and add it to -19 to get -24.
Take -8 from -10. Change the -8 to +8 and add to -10 to get -2.
Take +4 from +9. Change the +4 to -4 and add to +9 to get +5.
.
Multiplying:
.
If the signs of both numbers are positive or the signs of both numbers are negative,
multiply the numbers and give the answer a + sign.
.
If the signs of the two numbers are different (one + and one -), multiply the numbers
and give the answer a negative sign.
.
Dividing:
.
Basically the same as multiplying. Same signs, divide the two numbers and give the answer
a plus sign.
.
If the two numbers have different signs (one + and one -), divide the numbers and give
the answer a negative sign.
.
Hope this helps you with working out problems like the two you were given.
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