Let x----------> number of weeks y----------> saved money
we now that
<span>Michael begins with $20 and saves $5 per week so y=20+5x------> equation 1
and </span><span>Lindsey begins with no money, but saves $10 per week </span><span>y=10x-------> equation 2
</span><span>the number of weeks it will take for Lindsey and Michael to save the same amount of money is when equation 1 is equals to equation 2 </span> therefore 20+5x=10x------> 10x-5x=20------> 5x=20-----> x=20/5-----> x=4 weeks
9:2 is equivalent because it is dividing each side by the same amount. 18 divided by 2 is 9 and 4 divided by 2 is equal to 2, so 9:2 would be equivalent to 18:4.