This May be a Trick
Negative Thinking
Central Sum
100
Hockey Stick and ball cost $50. If the Stick cost $49 more than the ball. What is the cost of each ?
What is Hockey Stick $49.50 & ball $0.50
100

Tony owes Tina 40 cents
Then Tina borrows 50 cents from Tony.
Later Tony lends Tina 60 cents.

Who has to pay what to whom to square things up?

Answer: Tina owes Tony 70 cents

https://nrich.maths.org/6234/solution

100

Find all the whole numbers in the 900s where the middle digit equal to the sum of the other two digits.

990

200
Find three positive whole numbers that have the same answer added together or when multiplied together.
What is 1,2, & 3 1 x 2 x 3 = 6 and 1 + 2 + 3 = 6
200

Which of the following numbers is the product of exactly 3 distinct prime numbers?

45,   60,   91,   105,   330


Answer: 105
105 = 3 x 5 x 7

200

Find all the whole numbers in the 400s where the middle digit equal to the sum of the other two digits.

440, 451, 462, 473, 484, 495

300
Can you arrange four nines to make it equal to 100. Hint: use two mathematical symbols.
What is 99+9/9 = 100
300

I have some strange dice: the faces show the numbers 1 to 6 as usual, except that the odd numbers are negative (i.e. -1, -3, -5 in place of 1, 3, 5). If I throw two such dice, which of the following totals cannot be achieved? a) 3 or b) 7 or c) 8?

b) 7

300

Find all the whole numbers in the 300s where the middle digit equal to the sum of the other two digits.

330, 341, 352, 363, 374, 385, 396

400

Replace the '?' by any mathematical symbol to make the expression equal to 99. 18 ? 12 ? 2 ? 3 = 111

What is 18 x 12 ÷ 2 + 3 = 111

400

If the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 are all multiplied together, how many zeros are there at the end of the answer?

two zeros

You could write this problem out as 1×3×4×6×7×8×9×(2×5)×10. The product of the first seven numbers is not a multiple of ten, but the last part gives us 10×10 so the overall product must be a multiple of 100, but not a multiple of 1000. So the answer is two zeros.

400

Find all the whole numbers in the 200s where the middle digit equal to the sum of the other two digits.

220, 231, 242, 253, 264, 275, 286, 297

500
Divide 110 into two parts so that one will be 150 percent of the other. What are the 2 numbers?
What is 44 and 66
500

A quiz has twenty questions with 7 points awarded for each correct answer, 2 points deducted for each wrong answer and 0 for each question omitted. Jack scored 87 points. How many questions did he omit?

Answer: Jack omitted 5 questions.
Jack must have scored at least 87 points from his correct answers.
12 correct × 7 = 84 points
13 correct × 7 = 91 points
91 points − (2 wrong × 2) = 87 points.
So Jack could have got 13 right, 2 wrong and omitted 5

500

Find all the whole numbers in the 100s where the middle digit equal to the sum of the other two digits.

110, 121, 132, 143, 154, 165, 176, 187, 198

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