That evening after dinner at the kitchen table, Dezi plucked up all her courage. What if they just brushed her off as usual, and refused to listen? Or got annoyed?

“Ma and Dad, Granny, please can we all stay at the table and you let me show you something? Something to do with maths and numbers? And it comes with a story.”

They all turned to look at her, surprised. Maths and numbers? A story? What on earth did she want to do? None of them cared a damn about ‘maths and numbers’.

“Aww, but it is our show on TV now,” whined Maggie.

“And I promised to phone Nono. She’s feeling depressed; lockdown is so getting to her.”

Dezi’s Mom could sense that this was very important to her daughter; this clever daughter who already understood way more than she herself ever had about numbers. “Of course, Dezi, if you think it is important. What do you want to show us?”

“Let me just get the rice, and a chess board that I made.”

The others looked puzzled, Maggie and Tammy stifling giggles. Rice? Their sister really was a wierdo.

“Oh I know! She’s going to tell us that fable I once learned in school. The king and the wise old man,” said Rico.

“Hm? I don’t know it,” said Granny.

“Me neither,” said the younger girls in unison.

Dezi came back and laid out the home-made paper chess board. It had extra-big squares. She had her school bag stuffed full of something next to her, and held a small cup with a bit of rice in it.

She was pleased to see her audience all looking curious, even though her younger sisters were still giggling.

“So you know we have been ordered to go into lockdown, stay inside whenever possible, to stop the spread of the COVID-19 virus, right? And I am thinking that maybe you guys don’t understand the problem here, cos some of you are, like, breaking the rules. Actually, it’s an emergency law, not a rule. You’re breaking the law.”

“What? Who’s breaking the rules?” demanded her dad. “Although I must say, they do seem a bit much. Especially the part about no alcohol. Another day with no nice cold beer before supper.”

“Sorry Dad, but it just shows how serious it is. They want everyone to be really, you know, on it, and disciplined.”

“And not abusing their poor wives when home all day and drunk, like you-know-who across the road!” said her mom.

“And guys, I am afraid I have to piemp … cos I am so worried. I have to tell someone. Maggie went out to meet a friend. Rico went out to meet his girlfriend. And you know what that means about physical distancing … not! And Granny met three friends to pray.”

Now her father looked alarmed. “Are you all crazy!? The army is out there to arrest you!”

Her mother’s eyebrows had shot up and she also looked shocked. “Rico, Ma?”

“Well, you agreed Maggie could go out, Ma, so why not me?” retorted Rico.

“Okay okay … let’s not go over all that now,” said Dezi. “What’s done is done. Let me show you my thing, and then hopefully you’ll see why we must be super strict.

“First though, you know how a meme or clip goes viral on social media? Well, this is what a pandemic is: a virus going viral. Country to country viral, whole world viral. Virus, like COVID-19 virus, is where the word ‘viral’ comes from. And I’ll tell you this famous story to kinda show you how viruses spread.”

Dezi picked up some grains of rice.

“So there once lived a mega rich king and he loved playing chess. Or draughts, if you like, on a board like this. One day a wise old travelling man passed by and the king challenged him to a game. The wise old man was super good at chess, having played with people all over the world, so he said ‘Sure’. To add gees, and motivate him, the king offered him any reward he wanted, if he won. The old man asked for something strangely simple.

“He said, ‘If I win you must just count out grains of rice for me, like this. Put one grain on the first square, then double it on the second. Then double that one on the next, and so on, until the 64 squares of the chess board are full. The king thought he was stupid.

“Sure enough, the old man won, and the king began to award him his prize.

“But now, instead of kings and wise men and grains of rice, I want you to imagine each grain of rice is a person with coronavirus. And each infected person infects just one other person, that is, doubles their infection. So, one person infects one more, making two. And if two people each infect one other person, that makes 4 infected, and doubling that makes 8, and doubling that makes 16.”

As she spoke, Dezi put 1 grain on the first square, 2 on the second, 4 on the third, 8 on the fourth, and 16 grains on the fifth square.

At this point, she paused and brought out a plastic sandwich bag, with grains of rice in it.

“From here on, I have had to pre-count out the right number of grains into bags, because the numbers are getting too big to count out one-by-one for you. You’ll get bored!” She put the bag on the sixth square.

“So, there are 32 on the sixth, and 64 on the seventh, 128 on the eighth square, 256 on the ninth, 512 on the tenth, and 1024 on the eleventh.” On each square she put fuller and fuller bags of rice.

“And now I am just going to read you the numbers because no ways could I count out real grains: 2048 on the twelfth, 4096 on the thirteenth, 8 192 on the fourteenth, 16 384 on the fifteenth, 32 786 on the sixteenth, 65 536 on the seventeenth,  131 072 on the eighteenth, 262 144 on the nineteenth, 524 288 on the twentieth, and 1 million and 48 thousand 576 on the twenty-first square. By the 40th square it would be about 1 000 million! And we are nowhere near the end of the board.

“Right now, we in South Africa are at the beginning of the chess board. But our numbers are gonna rise and rise, faster and faster, just like they did in China, and are now doing in Europe and the US. The virus does not care about who you are. It just takes one person to come here and bring the first infection.”

The family all sat silent.

“Yoooo!” said Granny. “My brain is cracking to take in these numbers! But if you say so … and I mean … I can now see with my own eyes.”

“But is this for real?” asked Maggie. “I mean, it seems ridiculous.”

“Why don’t you check my sums on your phone’s calculator?” said Dezi. “You can do that while I arrange my ‘virus rice’ for my next ‘show and tell’,” she said, using air quotes. “I found this awesome thing on the internet.”

“Ja, I will,” said Mags.

“Me too,” said Tammy. “Race you! Let’s start from doubling 32 equals 64.”

As the younger girls did the calculations and competed to read out the answers, Dezi laid out her grains of virus rice on the table. She put them in a linear pattern, with branches.

She started with 1, then from that laid out 2 grains, and from each of those 4, like a tree diagram with two main branches. The sets of 4 grains then each became 8, and they each became 16. Then she waited until her sisters finished.

“Sjoe! Okay, I’m on to the twenty-first and you’re right. It’s over a million! Unreal,” exclaimed Tammy.

“Yup. Me too,” said Mags.

“This is called exponential growth,” said Dezi. “And unstoppable exponential growth is where this virus will be at, here in Mzansi, unless we do something.”

***

Tell us: Do you understand exponential growth? Or do you need to prove it to yourself, like Mags and Tammy did on their phone calculators?