need help with my 4th grader math homework

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Liz91899

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Oct 4, 2011
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Mario replaced 72 tires on the small and large trucks in his fleet. He replaced 3 times as many tires on the large trucks as on the small. How many tires did he replace on the small trucks?

I am stuck trying to do the math...

Liz
(parent)
 
What math were you trying, when you got stuck?


Here is an example:

I own 36 cars; some are red, and the rest are blue. There are three times as many red cars as blue. How many blue cars do I own?

To say that one number is three times bigger than another implies that the first number is 3/4ths of their total.

Or, said another way, 3/4ths of some total is three times as much as 1/4th of the total.

In my example, 3/4ths of the 36 cars are red. I will note the red cars inside parentheses:

(9 + 9 + 9) + 9 = 36

27 red + 9 blue = 36 total

Do you see? 27 is three times as much as 9.



I hope that my brief example jump-starts your imagination, but, if not, please show us what the fourth-grader tried. :D
 
Liz91899 said:
Mario replaced 72 tires on the small and large trucks in his fleet. He replaced 3 times as many tires on the large trucks as on the small. How many tires did he replace on the small trucks?

I am stuck trying to do the math...

Liz
(parent)
Click to expand...

At the fourth grade level, your child may be expected to use the "guess and check" method of problem solving.

This method involves GUESSING at a solution, then CHECKING to see if it fits the conditions of the problem. If it does not, you can "adjust" your guess and try again.

For example, we are trying to find how many tires were replaced on the small trucks. Suppose we GUESS that 20 tires were replaced on the small trucks. The problem says that "three times as many tires were replaced on the large trucks as on the small trucks." So, if we replaced 20 tires on the small trucks, then we must have replaced 3 * 20, or 60 tires on the large trucks. How many tires were replaced in all? 20 + 60 = 80, so we would have replaced a total of 80 tires. BUT....the problem says that the total number of tires replaced was 72, so we've got too many (this is the CHECK part)! What that means is that we need to pick a smaller number of tires for the small trucks. You can keep guessing and checking until you find a number that works.

I hope this helps you.
 
Liz91899 said:
Mario replaced 72 tires on the small and large trucks in his fleet. He replaced 3 times as many tires on the large trucks as on the small. How many tires did he replace on the small trucks?

I am stuck trying to do the math...

Liz
(parent)
Click to expand...


Let 3x = large truck tires

Let x = small truck tires


3x + x = 72


4x = 72

x = 72/4

x = 18

He placed 18 tires in the small truck and 3(18) as many or 54 tires in the large truck.


 
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