Question

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

Answer 1

total height = 21 inches = H
height of one = 1 3/4 =1.75 inches = h
total board = H/h = 21/1.75 = 12
so,
there are 12 boards.

Answer 2

Number of boards in the Stack is 12

Given:

A stack of board is 21 inches

Each of board is 1 3/4 inches

To find:

Number of boards

Solution:  

Given width of 1 board = 1 3/4 inches

⇒ 1 3/4 =  $\frac{7}{4}$ inches   [ (4 × 1) + 3 = 7 ]  

Let x be the number of boards in a stack

Then width of x boards =  $\frac{7x}{4}$  

From given data width of a stack of boards is 21 inches

⇒ $\frac{7x}{4} = 21$  

⇒ 7x = 84

⇒ x = 12

Therefore, Number of boards in the Stack = 12

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