Question

There are 25 desks in a classroom. The number of rows is five less than twice the number of desks in each row. Find the number of rows and the number of desks in each row.

Answer 1

if you think of every desk as a unit of the classroom than you get a box/rectangle of desks/units, so you end up with the Area of a rectangle equation

\[A=LW\]
\[25=LW\]

Answer 2

Let r = number of rows
Let d = number of desks per row

"The number of rows is five less than twice the number of desks in each row."
r = 2d - 5

"There are 25 desks in a classroom."
The number of desks, 25, is the number of rows multiplied by the number of desks per row, so
rd = 25

Since we have that r = 2d - 5, substitute:

(2d - 5)d = 25

Solve the equation for d

Answer 3

\[2d ^{2}-5d-25=0\] ??

Answer 4

Correct. Now solve the equation.

Answer 5

so d=-5/2 and d=5
throw away the negative value and you have d=5

Answer 6

that would equal the number of desks per row, what is the equation for number of rows?

Answer 7

oh wait, D=5 and R=5 ??

Answer 8

correct

Answer 9

thanks!