The easiest way to think of these is to put them in terms of percentages. Obviously, if you are SAVING 25%, you are SPENDING 75%. So if she SPENDS 13.50, we can easily use the 75% in an equation. $13.50 = .75x, with x being what the shoes cost originally. The .75 indicates that she is spending 75% of what the original cost is. You don't have any examples to pick from, but this is the best way to explain what one of the equations could be. You could also base it on money saved, but the equation is not quite as neat.
(2x-3)(5x-1). I Think that is the answer.
$27 x 18 students = 486 actual cost.
$30 x 10 students = 300 estimated total cost using compatible numbers.
$20 x 20 students = 400 estimated total cost using compatible numbers. (better option because it is nearer to the actual cost)
Compatible numbers are numbers that can easily be multiplied or divided using mental computation.
Compatible number for 27 and 18 can be: 30 and 20 OR 20 and 20 OR 30 and 10 OR 20 and 10.
However, there is a rule in multiplying the compatible numbers, when one number is increased the other number must be decreased.
So 27 can be increased to 30; while 18 can be decreased to 10 to get a product of 300.
27 can be decreased to 20; while 18 can be increased to 20 to get a product of 400.
That you and her have a 50% chance of winning.
