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This Week From Bedtime Math: Pick a Pack of Prickly Pear

Things get a bit thorny in today's math challenge.
on July 30, 2013


If you've ever tried to touch a cactus, it probably wasn't so easy, given all those spiky prickles.  Those prickles are actually the cactus' leaves, and they're skinny so they have less area to dry out in the sun, because cacti live in very hot places. But despite the spikes, you can eat some kinds of cactus, like the prickly pear plant shown here. The little flowers sprouting from the edges of some of those paddles will turn into fruit, called prickly pear figs. You can eat that fruit, and you can also eat the paddles themselves. But the paddles and the figs are covered with really teeny prickles, too, so you have to peel them carefully…beware when taking a bite out of cactus, or it might take a bite out of you. Now try challenging your children with these prickly pear math problems:

Wee ones: If a prickly pear paddle grows 1 new flower each day, and has been sprouting flowers for 5 days, how many will it have the next day?

Little kids: If a prickly pear paddle has flowers numbered 1 through 9, and birds eat the multiples of 2, which flowers are left to turn into fruit?  Bonus: If in picking each of those fruits you get 4 prickles stuck in you, how many prickles do you have to pluck out of you afterwards?

Big kids: That cactus has a lot of paddles and prickles, all growing from thick, woody, dried-out branches growing out of the center trunk.  If the 4 branches each have 6 sets of 5 paddles, how many funny flat paddles are there? Bonus: If each paddle has 20 prickles on each of its 2 sides, how many prickles does this plant have in total?

Wee ones: 6 flowers.

Little kids: Only flowers 1, 3, 5, 7, 9 are left.  Bonus: 20 prickles, from the 5 fruits.

Big kids: 120 paddles.  Bonus: 4,800 prickles!

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