T he Main Challenge
Here’s another selection of mental arithmetic questions. Can you answer all seven correctly?
- (10 + 10) – (15 – 3) = ?
- What is the sum of 0.83 and 0.89?
- What is 1 × 9?
- If Ben earns £10 every half-hour, how much will he earn in 40 hours?
- If you burn 100 calories by climbing 100 stairs, how many calories would you burn when climbing 50 stairs?
- What is 5,456 – 4,372?
- Twice my age plus 4 more is 72. How old am I?
The 7puzzle Challenge
The playing board of the 7puzzle game is a 7-by-7 grid containing 49 different numbers, ranging from 2 up to 84.
The 2nd & 5th rows contain the following fourteen numbers:
6 7 8 16 17 21 28 48 50 55 63 64 81 84
What is the product of the two prime numbers?
The Lagrange Challenge
Lagrange’s Four-Square Theorem states that every positive integer can be made by adding up to four square numbers.
For example, 7 can be made by 2²+1²+1²+1² (or 4+1+1+1).
There are just THREE ways of making 104 when using Lagrange’s Theorem. Can you find them?
The Mathematically Possible Challenge
Using 5, 7 and 10 once each, with + – × ÷ available, which are the only TWO numbers it is NOT possible to make from the list below?
25 35 45 55 65 75 85 95 105 115
#MultiplesOf5
The Target Challenge
Can you arrive at 104 by inserting 2, 4, 12 and 15 into the gaps on both lines?
- (◯–◯)×(◯–◯) = 104
- ◯×(◯+◯)–◯² = 104
Answers can be found here.
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