Question

A rectangle has a length of 9.00 inches and a width of 4.25 inches. What is the area in square inches. Round to the correct significant digits

Answer 1

Let the length of a rectangle be l and the width of that rectangle be w, then the area of the rectangle is given by:

                           $A_{rectangle}=l\cdot w$

In our problem, l= 9 inches, and w=4.25 inches.

then, 

$A_{rectangle}=l\cdot w=9 \cdot 4.25=9\cdot(4+0.25)=9\cdot4+9\cdot0.25\\\\=36+2.25=38.25$ (square inches)

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Remark: we performed the following operation to make the multiplication easier:

$9 \cdot 4.25=9\cdot(4+0.25)=9\cdot4+9\cdot0.25$

we wrote 4.25 as 4+0.25, and multiplied 9 to each of these separately, instead of multiplying 9 to 4.25 directly, using the distributive property

thus making the operation a little easier.
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Answer: 38.25 square inches


Remark : 

Asking "Round to the correct significant digits" is not correct. 

The number of significant digits must be stated. 

if we want the number rounded to 3 significant digits 38.25 is 38.6 

if we want the number rounded to 2 significant digits 38.25 is 38.0 

if we want the number rounded to 1 significant digits 38.25 is 40,0