You can use money to buy food, clothes, and other things you need, but you can also buy stuff you definitely don’t need. On the website eBay, you can get eyelashes for your car or sunglasses for your dog (“Doggles”). The catch is, everyone who wants to buy an item “bids” on it: they secretly say how many dollars they are willing to pay, and whoever bids the most dollars wins and buys it. It all depends how badly your dog wants shades!

*Wee ones:* If you bid $5 for those Doggles and your friend bids $4, which of you bid more? Who will get to buy them?

*Little kids:* If you buy a green striped singing stuffed elephant for $6, and someone buys it from you for $8, how much more money do you have now than before you bought it? *Bonus:* If someone else suddenly bid $5 more than the $8 bid, how much money will that person pay you?

*Big kids:* You can buy Doggles in 12 different colors. If they have 1 yellow pair in stock but 2 pairs of each of the other colors, how many pairs do they have? *Bonus:* The car eyelashes sold for $13.99. If you had bid double that, how much would you have paid for them? (Hint if needed: If they had been exactly $14, how different would your answer be?)

*The sky’s the limit: *If you buy 5 pairs of Doggles each in a different color — say red, yellow, blue, green and black — and you and your dog each choose a pair to wear, how many different color combos could the two of you be wearing?

Answers:*Wee ones:* You bid more, since 5 is more than 4, so you’ll get to buy them!

*Little kids:* $2 more. *Bonus:* $13.

*Big kids:* 23 pairs, since they’d have 24 if they had 2 of each. *Bonus:* $27.98.

*The sky’s the limit: *20 different combinations. For each of the 5 colors you wear, there are 4 remaining colors from which your dog can choose. If you wear red, your dog can wear yellow, or blue, or green, or black, making 4 combos. If you instead wear yellow, then your dog could wear red, blue, green, or black, adding another 4…and so on. By the time you try all 5 colors, you’ve created 5 sets of 4 combos, making 20 total.