Question

WILLL MEDAL
Holly finds that (11m – 13n + 6mn) – (10m – 7n + 3mn) = m – 20n + 9mn. What error did Holly make?
a)he only used the additive inverse of 10m when combining like terms.
b)She added the polynomials instead of subtracting.
c)She only used the additive inverses of –7n and 3mn when combining like terms.
d) She did not combine all like terms.
please helppp

Answer 1

@perl

Answer 2

@dan815

Answer 3

@shrutipande9

Answer 4

@jim_thompson5910

Answer 5

@phi

Answer 6

start with
(11m – 13n + 6mn) – (10m – 7n + 3mn)

the minus sign in front of (10m – 7n + 3mn)
means we subtract *every* term inside the parens (think of it as a package of stuff, and we are "taking away" everything listed in the package

in other words, replace -(10m – 7n + 3mn)
by multiplying each term by -1. can you do that ?

Answer 7

3mn+m-6n?

Answer 8

I like to do these problems in small steps (because we have to figure out what went wrong)

replace -(10m – 7n + 3mn) by multiplying each term by -1.
can you do that ?

Answer 9

10+7n-3mn

Answer 10

-10+7n-3mn

Answer 11

ok except it's -10m (not just -10, right?)

Answer 12

-10m+7n-3mn my bad lol i forgot

Answer 13

ok, that means
(11m – 13n + 6mn) – (10m – 7n + 3mn)
can be written as
11m – 13n + 6mn -10m+7n-3mn

now look at the terms with just "m"
11m - 10m
that says, we have 11 m's take away 10 m's. How many m's do we have ?

Answer 14

-m right because its -1m

Answer 15

you have 11 apples and take away 10 apples. How many apples do you have ?

Answer 16

1m

Answer 17

yes, 11m - 10m is 1m or just m (we don't bother putting in the one)
Holly got m, so she did that part correctly

Answer 18

11m – 13n + 6mn -10m+7n-3mn

now look at just the terms with "n"
-13n + 7n
any ideas ?

Answer 19

she didnt combine all like terms right .-.??

Answer 20

first what is -13n + 7n ?

Answer 21

-6n

Answer 22

what did Holly get ?

Answer 23

she got -20

Answer 24

-20n (don't forget the letters)

Answer 25

if the error were "did not combine all like terms"
you would see (for example)
-13n + 7n in her answer
(because she would have two "like terms" (both have the same letter) that she did not combine)

but Holly's answer shows all the like terms combined. (but obviously -20n is not correct)

Answer 26

she must have done -13n -7n which gives -20n
so she used -7n instead of +7n

Answer 27

she did get the m term correct
but the other two terms look wrong

Answer 28

that would be c because she used -7n

Answer 29

using the "additive inverse" is the correct thing to do
(the language is confusing, isn't it?)

Answer 30

yeah ._. so did i get it rightt??

Answer 31

if she uses the additive inverse, she would get the correct answer
she got the wrong answer. that means she did not use the additive inverse.

Answer 32

which term did Holly get correct ? the m term
she used the additive inverse for that term

Answer 33

ohhh its a because she only added the 10m and got that one right but didnt do it to the rest

Answer 34

exactly