Power Play (Exponents) | A

Question 1

How many times can you fold it over and over?

Estu says “I heard that a sheet of paper can’t be folded more than 7 times”.

Roxie replies “What if we use a thinner paper, like a newspaper or a tissue paper?”

Try it with different types of paper and see what happens.

Question diagram 1
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Solution
Understand the Question
  • Every time a sheet of paper is folded in half, its thickness doubles and its surface area halves: this is an example of exponential growth, given by Tn=T0×2nT_n = T_0 \times 2^n.
  • While theoretical thickness increases rapidly to astronomical scales in just tens of folds (e.g. 4246\approx 42\text{--}46 folds to reach the Moon), physical limits—such as rapidly increasing stiffness and dwindling surface area—limit practical folds to around 787\text{--}8 times for standard paper, and up to 1212 times for very thin, large paper.

Step 1 · Exponential Growth in Thickness

Diagram 1

Let standard initial paper thickness be T0=0.1 mmT_0 = 0.1\text{ mm}. With each fold, thickness doubles:

After 1 fold: 0.1 mm×21=0.2 mm0.1\text{ mm} \times 2^1 = 0.2\text{ mm}

After 2 folds: 0.1 mm×22=0.4 mm0.1\text{ mm} \times 2^2 = 0.4\text{ mm}

After 3 folds: 0.1 mm×23=0.8 mm0.1\text{ mm} \times 2^3 = 0.8\text{ mm}

After 4 folds: 0.1 mm×24=1.6 mm0.1\text{ mm} \times 2^4 = 1.6\text{ mm}

Step 2 · Calculate Theoretical Thickness After 46 Folds

Given initial thickness T0=0.1 mm=104 mT_0 = 0.1\text{ mm} = 10^{-4}\text{ m} and distance to the Moon 384,400 km=3.844×108 m\approx 384,400\text{ km} = 3.844 \times 10^8\text{ m}.

Thickness after nn folds is Tn=T0×2nT_n = T_0 \times 2^n.

For n=46n = 46 folds: T46=104 m×246T_{46} = 10^{-4}\text{ m} \times 2^{46}

Since 2101032^{10} \approx 10^3: 246=26×(210)464×(103)4=64×10122^{46} = 2^6 \times (2^{10})^4 \approx 64 \times (10^3)^4 = 64 \times 10^{12}

T46104 m×64×101264×108 m6.4×109 m\begin{aligned} T_{46} &\approx 10^{-4}\text{ m} \times 64 \times 10^{12} \\[0.6em] &\approx 64 \times 10^8\text{ m} \\[0.6em] &\approx 6.4 \times 10^9\text{ m} \end{aligned}

Since 6.4×109 m>3.844×108 m6.4 \times 10^9\text{ m} > 3.844 \times 10^8\text{ m}, the paper theoretically exceeds the distance to the Moon.

Step 3 · Analyze Practical Physical Limitations

In practice, folding is limited by physical constraints:

  • Exponentially increasing thickness: Each fold doubles the thickness and substantially increases the force required to crease.
  • Shrinking surface area: Each fold halves the area, leaving insufficient perimeter to wrap around the crease.

For a standard sheet of paper (like A4), the limit is typically 77 to 88 folds. Using thinner, larger sheets (like newspaper or tissue paper) allows up to 99 to 1212 folds.

Answer

Practically, standard paper can be folded 787\text{--}8 times, while thinner/larger paper can reach 9129\text{--}12 times. Theoretically, thickness doubles exponentially (Tn=T0×2nT_n = T_0 \times 2^n) and reaches astronomical distances in tens of folds.

Common Mistakes
  • Linear vs. Exponential Growth: Assuming thickness grows by adding a constant layer each time instead of multiplying by 22 (2n2^n) at every fold.
  • Overlooking Area Loss: Forgetting that folding also halves the available surface area, which is the primary physical constraint that stops further folds.

More questions in A

Q1

How many times can you fold it over and over?

Estu says “I heard that a sheet of paper can’t be folded more than 7 times”.

Roxie replies “What if we use a thinner paper, like a newspaper or a tissue paper?”

Try it with different types of paper and see what happens.

Q2

Think about how many combinations are possible in different contexts. Some examples are—

(i) Pincodes of places in India—The Pincode of Vidisha in Madhya Pradesh is 464001. The Pincode of Zemabawk in Mizoram is 796017.

(ii) Mobile numbers.

(iii) Vehicle registration numbers.

Try to find out how these numbers or codes are allotted/generated.

Q3

Tremendous in Ten!

Find a partner to play this game with. In 10 seconds, the person who writes a number or an expression, using only the digits 0-9 and arithmetic operations, that gives a number that is the larger between the two wins the round.

Below are some conditions that you may consider for different rounds.

(i) Exponents are not allowed. Only addition is allowed.

(ii) Exponents are not allowed. Only addition and multiplication are allowed.

(iii) Exponents are allowed. Only addition is allowed.

(iv) Exponents are allowed. Any arithmetic operation is allowed.

You can create your own conditions and/or involve more people to play together.

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