The Count's Staircase: Arithmetic progressions comic

LearnFun Comics#46
The Sum Goblin

The Count's Staircase

Stairs go up, but not too high! Or do they?

Starring Momo
Arithmetic progressions ยท Class 10

Numbered Steps Park. Momo plays on the stairs.

Momo: Five steps to the top. Easy peasy!

The Sum Goblin

The Sum Goblin: Ah, the nth step. You'll need to climb more each day!

Momo: More steps? But how many? And which day? Oh no!

Steps add up

Steps change daily same.

Climb higher each time.

Arithmetic Progression!

Momo: So each day, the steps get higher? Just by the same number?

The Sum Goblin

The Sum Goblin: Day 1: 3 steps. Day 2: 5 steps. Day 3: 7 steps! See the pattern?

Momo: Like climbing 2 steps each day. 3, 5, 7... see the pattern?

Day 1: 3 steps

Day 2: 5 steps

Day 3: 7 steps

Momo's trick

Day n means: a + (n-1)d

For day 50: a + 49d

It's like counting in steps!

Momo: To find day 50, use a + 49d. Easy peasy!

Your turn, hero!

The Sum Goblin
The Sum Goblinโ™ฅโ™ฅโ™ฅ

Day 1: 1 step. Day 2: 3 steps. How many steps on Day 10?

19. 1 + (10-1)ร—2 = 19.

The Sum Goblin

The Sum Goblin: Day 50: 101 steps! Pay up, moocher!

10 steps daily. Day 50: how many steps?

500. 10 + (50-1)ร—10 = 500.

The final battle

The Sum Goblin
The Sum Goblinโ™ฅโ™ฅโ™ฅ

If Day 1 costs โ‚น10 and Day 50 costs โ‚น500, what is the daily increase in toll? answer: 9

10. (500-10)/49 = 10

The Sum Goblin

The Sum Goblin: You can't add 100 steps! My plan is a joke!

Momo: Day 50: 101 steps. Not a joke, but a rule! 3 plus 2 times (50-1).

By noon, all 101 steps were paid. And the goblin was learning.

The End?

Remember

  • Each day adds the same number.
  • Use a + (n-1)d to find any day.
  • It's like counting in steps!

But what's next? The goblin's note falls. 'Next problem: Fibonacci!'

A comic book about Arithmetic progressions. Follow Momo, learn the idea, and answer three questions to beat The Sum Goblin.

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