# Use algebra with segment lenths

#### ErickaS

##### New member
I am confused on how to help my daughter with this! The example gives an equation to use but the actual questions don’t. I don’t want answers but I would like it to be explained better so I can help her do the work.

#### Jomo

##### Elite Member
M is the midpoint which cuts the line segment into 2 equal pieces.

These are the facts that you should know below.

1) The left half equal the right half.
2) The left half is half of the entire length.
3) The right half is half of the entire length
4) The entire length is twice the right half.
5) The entire length is twice the left half.

To challenge your daughter's understanding of the above rules you should state the above rules one at a time leaving out the underlined word. She should tell you the missing word.

When she can answer those questions above with true understanding then she will have no trouble do the assignment.

#### Subhotosh Khan

##### Super Moderator
Staff member
View attachment 17431I am confused on how to help my daughter with this! The example gives an equation to use but the actual questions don’t. I don’t want answers but I would like it to be explained better so I can help her do the work.
You have to use the fact that

the mid-point divides a straight line into two equal parts, and,

The total length of the original line is twice that of the each individual part.

#### Jomo

##### Elite Member
Another point I want to add. Wherever a distance is unknown you can call it x. Maybe that is what are looking at.

For example in #5, AM = x and BM = x
In #6, ML=x

I just look more closely at the problem set and all I have to ask is who writes these problems!? The example labels the problem with x or x+6 but then the exercise for that example do not have any x's. Simply amazing!

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#### ErickaS

##### New member
Thank you! I am confused on why the example didn’t match the actual problems too. A lot of her work is like that.

#### ErickaS

##### New member
My 3rd graders math homework focused on time. But the questions seemed backwards too.
______ + 1hr and 45 minutes = 9:30
REALLY? I barely figured it out let alone having my son be able to do it. School these days seem to teach things weird compared to when I went.

#### Jomo

##### Elite Member
Thank you! I am confused on why the example didn’t match the actual problems too. A lot of her work is like that.
That is so terrible that the examples do not match the problems set. Can you get her a better good that matches what she is being taught in school? It irritates me so much when I hear about books like this. My daughter's book had three definitions on one page and two of the three were outright wrong.

#### Jomo

##### Elite Member
My 3rd graders math homework focused on time. But the questions seemed backwards too.
______ + 1hr and 45 minutes = 9:30
REALLY? I barely figured it out let alone having my son be able to do it. School these days seem to teach things weird compared to when I went.
The question is asking the following. What time is it now if in 1 hr 45 min it will be 9:30. This is a subtraction problem.

Consider this simpler question. What number to 2 equals 17. One would usually think that the unknown number can be found my computing 17-2.

Your son should compute 9:30 - 1:45

If you have trouble explaining this to your son let us know.

#### Otis

##### Senior Member
… What number to 2 equals 17.
Jomo meant to write:

What number added to 2 equals 17?

$$\;$$

#### Otis

##### Senior Member
… School these days seem to teach things weird compared to when I went.

We can borrow when subtracting times given in hours and minutes. When we borrow 1 from the "hours column", we add it as 60 to the amount in the "minutes column".

Let us know, if you'd like to see an example of borrowing in standard subtraction and in time subtraction.

#### ErickaS

##### New member

We can borrow when subtracting times given in hours and minutes. When we borrow 1 from the "hours column", we add it as 60 to the amount in the "minutes column".

Let us know, if you'd like to see an example of borrowing in standard subtraction and in time subtraction.

Yes I very much would love to see an example!

#### Otis

##### Senior Member
… would love to see an example!
Sure, Ericka, but I still don't know whether your student understands the concept of borrowing (also called regrouping) in subtraction. Let's start with that. Here are two links. The written lesson has some nifty animations (plus worksheets), and the video lesson does a good job of showing place-value (by also writing the numbers expanded).

Written

Video

The concept of borrowing in time is similar. With hours and minutes, we have two columns.

10 : 45

The column on the right side of the colon is the minutes-column. To the left of the colon is the hours-column. If we borrow one unit of time from the hours column, then that's 60 minutes to add to the minutes-column. The first four minutes in the following video go through two examples.

Subtracting time

Let us know what the student's questions are.