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4 red, 2 purple and 1 yellow
Seven counters, three colours, red the most, yellow the least and purple only just ahead of yellow. 4 + 2 + 1 is the only way to split 7 like that.
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6/10 (or 3/5), which is 0.6
The shape is split into 10 equal parts and 6 of them are shaded. Six tenths is 0.6 as a decimal.
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13,468 and 86,431
For the smallest number, put the digits in order from smallest to largest. For the largest, go from largest to smallest.
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A heptagon
It has 7 sides. “Hepta” is the Greek word for seven.
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9:25am
10 minutes gets you from 8:50 to 9:00, and the other 25 minutes takes you to 9:25.
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23 and 35
Start at 11 and add 6 each time: 11, 17, 23, 29, 35, 41.
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25°
Angles around a point add up to 360°. The square corner is a right angle (90°), so x = 360 − 135 − 90 − 110 = 25.
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Haese Mathematics Readers. Building maths through storytelling
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4 km west of the harbour
8 + 7 = 15 km west, then 11 km back towards the harbour leaves it 4 km west.
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34 m²
Area of a triangle = ½ × base × height = ½ × 10 m × 6.8 m = 34 m².
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About 38 years
$1,000,000,000 ÷ $50 = 20,000,000 minutes. That’s about 333,333 hours, or 13,889 days, which works out to roughly 38 years.
The last 5 are proper brainteasers.
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27 cuts
9 cuts one way, 9 cuts the other way, then 9 cuts from top to bottom. 9 + 9 + 9 = 27, and you end up with 1,000 little cubes.
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2178
The first digit of the reversed number must be 8 or 9, so the final digit of the original number must be 8 or 9. However, 8 is the only possibility, since the reversed number ends in 2 (8 x 4 =32).
Since the reversed number starts with 8, the second digit of the original number must be 0,1, or 2. 1 is the only possibility, to ensure the reversed number is a multiple of 4 (ie it ends in 12).
Since 21x4=84, the remaining digit must be at least 4. By trying each possibility, the correct option is 7.
The original number is 2187, and 8712=4x2178.
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172 pages
The first 9 pages contain 1 digit each, for a total of 9 digits.
The next 90 pages contain 2 digits each, for a total of 180 digits.
The next n pages contain 3 digits each, for 3n digits in total.
9 + 180 + 3 n = 408
3n = 219
Therefore there are 9 + 90+ 73 = 172 pages -
3:45am
Call each candle 1 unit long. After t hours the 4-hour candle has 1 − t/4 left and the 5-hour candle has 1 − t/5 left. The slow one is four times the fast one when:
1 − t/5 = 4(1 − t/4)
1 − t/5 = 4 − t
5 − t = 20 − 5t
4t = 15
t = 3¾ hours3¾ hours after midnight is 3:45am. Check: the fast candle has 1/16 left and the slow one has 1/4, exactly four times as much.
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32 and 8/11 minutes (about 32 minutes 44 seconds)
Every minute the minute hand moves 6° and the hour hand moves ½°, so the gap between them grows by 5½° a minute. To get from one right angle to the next the gap has to change by 180°, and 180 ÷ 5½ = 32 8/11 minutes.
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