# Total Cost calculation

• Jul 24th 2011, 01:48 PM
KayPee
Total Cost calculation
Theresa bought lunch for herself and 2 friends. The cost for each lunch was between $3.95 and$4.80, including tax. Which of the following could be the total cost of the lunches that Theresa bought? A $9 B$13 C $18 D$26 Is the answer to the question above question $13 Total Cost(TC) = Average cost(AC) * Quantity (Q) = ( 3.95 + 4.8)/2 * 3 =13.125 How best can I explain the answer in a simple format to a grade 7 class? • Jul 24th 2011, 03:49 PM pickslides Re: Total Cost calculation Not sure if this will make things more confusing or not. Let $x$ be the cost of one lunch, we know $3.95 and there are 3 lunches in total so $3\times 3.95<3x<3\times 4.80$ $11.85<3x<14.4$ therefore the total cost must be$13 as none of the other options fit within the inequality.
• Jul 25th 2011, 06:05 AM
SpringFan25
Re: Total Cost calculation
if its for kids who haven't done inequalities before you could ask them to work out with you what the lowest possible cost is (3.95*3), then what the highest possible cost is (4.8*3), and then note that only \$13 is a possible answer.

which is identical to the previous post, with a gentle introduction