Math Blue Book p. 598 #13

Test Preparation SAT Preparation
1

<li>A school ordered $600 worth of lightbulbs. Some of the lightbulbs cost $1 each and the others cost $2 each. If twice as many $1 bulbs as $2 bulbs were ordered, how many lightbulbs were orderd altogether?</li>
</ol>

<p>(Here’s my solution, but can some of you tell me if my reasoning/equations are mathematically sound? thanks):</p>

<p>let x= # of bulbs</p>

<p>2x($1)+x($2)=$600
2x+2x=600
4x=600
x=150</p>

<p>3*150= (450) << answer</p>

2

<p>i got 450 too, but i did:
x= number of $1 bulbs y= number of $2 bulbs
1x + 2y = 600
-x + 2y = 0 ( since 2y = x)</p>

<p>4y = 600
y = 150
2(150) = x
300 = x
300 + 150 = 450</p>