a stack of boards is 21 inches high. each board is 1 3/4 inches thick. How many boards are there?

Question

6th grader. Mom here, having problem even remembering how to do this. 

Answer 1

First, turn the word problem into an equation you can solve.

 

Let h = the height of all the boards = 21 inches

Let x = the number of boards

Let t = the thickness of each board = 1 3/4 inches = 1.75 inches

 

We know that the number of boards * the thickness of each board = the total height.

So we can express this in an equation as follows:

 

x * t = h

 

We know t and h, so enter them in:

 

x * 1.75 = 21

 

Now you can solve for x.

 

Divide both sides by 1.75:

 

x = 21 / 1.75

 

x = 12

 

Therefore, there are 12 boards.

Answer 2

Divide 21 inches by 1 3/4 inches.

 

(21 inches) / (1 3/4 inches)

 

 

Then convert the mixed number to a improper fraction.  When dividing by fractions, multiply by the reciprocal.