Number Play

The sum of four consecutive numbers is 34. What are these numbers?

Suppose p is the greatest of five consecutive numbers. Describe the other four numbers in terms of p.

For each statement below, determine whether it is always true, sometimes true, or never true. Explain your answer. Mention examples and non-examples as appropriate. Justify your claim using algebra.

Find a few numbers that leave a remainder of 2 when divided by 3 and a remainder of 2 when divided by 4. Write an algebraic expression to describe all such numbers.

"I hold some pebbles, not too many, When I group them in 3's, one stays with me. Try pairing them up — it simply won't do, A stubborn odd pebble remains in my view. Group them by 5, yet one's still around, But grouping by seven, perfection is found. More than one hundred would be far too bold, Can you tell me the number of pebbles I hold?"

Tathagat has written several numbers that leave a remainder of 2 when divided by 6. He claims, "If you add any three such numbers, the sum will always be a multiple of 6." Is Tathagat's claim true?

When divided by 7, the number 661 leaves a remainder of 3, and 4779 leaves a remainder of 5. Without calculating, can you say what remainders the following expressions will leave when divided by 7? Show the solution both algebraically and visually.

Find a number that leaves a remainder of 2 when divided by 3, a remainder of 3 when divided by 4, and a remainder of 4 when divided by 5. What is the smallest such number? Can you give a simple explanation of why it is the smallest?

Find, without dividing, whether the following numbers are divisible by 9.

Find the smallest multiple of 9 with no odd digits.

Find the multiple of 9 that is closest to the number 6000.

How many multiples of 9 are there between the numbers 4300 and 4400?

The digital root of an 8-digit number is 5. What will be the digital root of 10 more than that number?

Write any number. Generate a sequence of numbers by repeatedly adding 11. What would be the digital roots of this sequence of numbers? Share your observations.

What will be the digital root of the number 9a + 36b + 13?

Make conjectures by examining if there are any patterns or relations between the parity of a number and its digital root, and the digital root of a number and the remainder obtained when the number is divided by 3 or 9.

If 31z5 is a multiple of 9, where z is a digit, what is the value of z? Explain why there are two answers to this problem.

"I take a number that leaves a remainder of 8 when divided by 12. I take another number which is 4 short of a multiple of 12. Their sum will always be a multiple of 8", claims Snehal. Examine his claim and justify your conclusion.

When is the sum of two multiples of 3, a multiple of 6 and when is it not? Explain the different possible cases, and generalise the pattern.

Sreelatha says, "I have a number that is divisible by 9. If I reverse its digits, it will still be divisible by 9".