Answer
The number of tiles at $\$1.25$ is $300$
and the number of tiles at $\$1.75$ is $420$.
Work Step by Step
Let the number of tiles at $\$1.25$ is $x$.
and the number of tiles at $\$1.75$ is $y$.
Total ceiling tiles are $=720$.
$\Rightarrow x+y=720$ ...... (1)
Total bill is $=\$1110$.
$\Rightarrow 1.25x+1.75y=1110$ ...... (2)
Multiply equation (1) by $-1.25$.
$\Rightarrow -1.25x-1.25y=-900$ ...... (3)
Add equation (2) and (3).
$\Rightarrow 1.25x+1.75y-1.25x-1.25y=1110-900$
Simplify.
$\Rightarrow 0.50y=210$
Divide both sides by $0.50$.
$\Rightarrow y=420$
Substitute the value of $y$ into equation (1).
$\Rightarrow x+420=720$
Subtract $420$ form both sides.
$\Rightarrow x=720-420$
Simplify.
$\Rightarrow x=300$
Hence, the number of tiles at $\$1.25$ is $300$ and the number of tiles at $\$1.75$ is $420$.
