
The Count's Staircase
Stairs go up, but not too high! Or do they?
Arithmetic progressions ยท Class 10

The Count's Staircase
Stairs go up, but not too high! Or do they?
Numbered Steps Park. Momo plays on the stairs.
Momo: Five steps to the top. Easy peasy!
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: 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!

Day 1: 1 step. Day 2: 3 steps. How many steps on Day 10?
19. 1 + (10-1)ร2 = 19.
The Sum Goblin: Day 50: 101 steps! Pay up, moocher!
10 steps daily. Day 50: how many steps?
500. 10 + (50-1)ร10 = 500.
The final battle

If Day 1 costs โน10 and Day 50 costs โน500, what is the daily increase in toll? answer: 9
10. (500-10)/49 = 10
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?

Villain card won! Answer again in a few days and it turns gold.
Remember
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.