Algebra Play | IT

Question 4

Context: In the date trick, the final answer is given by 100M+165+D100M + 165 + D, where MM is the month and DD is the day.

Q. Find the dates if the final answers are the following:

(i) 1269

(ii) 394

(iii) 296

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Solution
Understand the Question
  • The date trick formula is given by: Final Answer=100M+165+D\text{Final Answer} = 100M + 165 + D where MM represents the month number (11 for January, 22 for February, etc.) and DD represents the day of the month (11 to 3131).
  • Subtracting 165165 from the final answer isolates the date components: 100M+D=Final Answer165100M + D = \text{Final Answer} - 165
  • In the resulting number, the hundreds place gives the month MM, and the remaining two digits (units and tens) give the day DD.

(i) Find the date if the final answer is 12691269.

Step 1 · Calculate Month and Day for 1269

Substitute the final answer into the formula:

100M+D=1269165=1104\begin{aligned} 100M + D &= 1269 - 165 \\[0.6em] &= 1104 \end{aligned}

Separating the hundreds and the day:

M=11    NovemberD=4    4th\begin{aligned} M &= 11 \implies \text{November} \\[0.6em] D &= 4 \implies 4^{\text{th}} \end{aligned}
Answer

(i) 4th of November

(ii) Find the date if the final answer is 394394.

Step 1 · Calculate Month and Day for 394

Substitute the final answer into the formula:

100M+D=394165=229\begin{aligned} 100M + D &= 394 - 165 \\[0.6em] &= 229 \end{aligned}

Separating the hundreds and the day:

M=2    FebruaryD=29    29th\begin{aligned} M &= 2 \implies \text{February} \\[0.6em] D &= 29 \implies 29^{\text{th}} \end{aligned}
Answer

(ii) 29th of February

(iii) Find the date if the final answer is 296296.

Step 1 · Calculate Month and Day for 296

Substitute the final answer into the formula:

100M+D=296165=131\begin{aligned} 100M + D &= 296 - 165 \\[0.6em] &= 131 \end{aligned}

Separating the hundreds and the day:

M=1    JanuaryD=31    31st\begin{aligned} M &= 1 \implies \text{January} \\[0.6em] D &= 31 \implies 31^{\text{st}} \end{aligned}
Answer

(iii) 31st of January

Common Mistakes
  • Subtraction Error: Forgetting to subtract 165165 first before splitting the number into month and day.
  • Misinterpreting Digits: For a single-digit day such as in 11041104, incorrectly reading D=40D = 40 instead of D=4D = 4.
  • Swapping Month and Day: Mixing up MM (hundreds digits) and DD (last two digits), leading to invalid dates.

More questions in IT

Q1

Context: Think of a number trick:

  1. Think of a number.
  2. Double it.
  3. Add four.
  4. Divide by two.
  5. Subtract the original number you thought of.

Q. I predict you get 2. Am I right? Try it out with different starting numbers. Do you always end up with the same value, 2? Why?

Q2

Context: Consider the following number trick:

  1. Think of a number.
  2. Double it.
  3. Add four.
  4. Divide by two.
  5. Subtract the original number you thought of. (This trick always results in 2).

Q. How would you change this game to make the final answer 3? What about 5?

Q3

Context: Consider the following number trick:

  1. Think of a number.
  2. Double it.
  3. Add four.
  4. Divide by two.
  5. Subtract the original number you thought of. (This trick always results in 22).

Q. Can you come up with more complicated steps that always lead to the same final value?

Q4

Context: In the date trick, the final answer is given by 100M+165+D100M + 165 + D, where MM is the month and DD is the day.

Q. Find the dates if the final answers are the following:

(i) 1269

(ii) 394

(iii) 296

Q5

Context: In the date trick, the final answer is given by 100M+165+D100M + 165 + D, where MM is the month and DD is the day.

Q. Can you change the steps in this trick and still find the original date? Instead of subtracting 165 from the final answer, you might have to subtract some other number.

Q6

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Q8

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Q9

What is the relationship between the numbers in the bottom row and the number at the top?

Let us start with the simplest pyramid.

Q10

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Q11

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Q12

Context: 6.5 The Largest Product

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Q13

Context: Mukta's trick: Choose a 2-digit number of different digits, reverse the digits to get another number, find their difference, and divide the result by 9.

Q. If we choose other 2-digit numbers, and follow the steps, will there always be no remainder?

Q14

Context: Suppose a two-digit number is abab. When it is reversed, the new number is baba. If b>ab > a, the difference is baab=9(ba)ba - ab = 9(b - a), which is divisible by 9.

Q. Can you work out what happens if a>ba > b?

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