1.
Nusayba picks a basket of figs. She gives 6 of them to her brother. Then she finds 9 more on the path. She shares what she is carrying equally with a friend, keeping half, and ends up with 11 figs. How many did she pick to start with?
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Answer:
Did you know? Fig trees feed more rainforest animals than almost any other tree, because somewhere in the forest a fig is always ripe.
2.
There are 24 birds in a clearing. 13 of them are green. 11 of them can copy other sounds. 6 birds can do both. How many birds are neither green nor able to copy sounds?
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Answer:
Did you know? A toucan's huge beak is mostly hollow, full of air pockets, and it lets the bird dump heat like a radiator.
3.
3 monkeys eat 3 mangoes in 3 minutes. How long would 9 monkeys take to eat 9 mangoes? Think before you write. This one is not the calculation it looks like.
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Answer:
Did you know? Howler monkeys are the loudest land animal in the Americas — a troop can be heard about 5 km through thick forest.
4.
5 parrots sit in a tree. Each parrot calls to every other parrot exactly once. How many calls happen altogether?
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Answer:
Did you know? Wild parrots appear to use a signature call for each bird, rather like a name, and they learn it as chicks.
1.
Three researchers — Ibrahim, Khadija, and Sumayya — each study a different animal (toucan, jaguar, sloth) from a different camp (Canopy, Ridge, River). Who studies what, and from where?
1. The researcher at the Canopy camp studies the toucan. 2. Ibrahim is not at the River camp, and does not study the sloth. 3. Khadija studies the jaguar. 4. Sumayya is not at the Ridge camp.
SHOW YOUR THINKING
Answer:
Did you know? Sloths climb down to the forest floor only about once a week, and it is the most dangerous trip they make.
2.
Two frogs call on a steady beat. One calls every 8 seconds, the other every 14 seconds. They call together at exactly 6:00:00. How many seconds until they call together again? How many times will they call together in the first 5 minutes?
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Answer:
Did you know? Poison dart frogs build their poison from what they eat, so the same frog raised in a zoo is completely harmless.
3.
Someone let the last canoe drift away.
Umar says: "It wasn't me." Harun says: "It was Umar." Zaynab says: "It wasn't Harun."
Exactly one of the three is telling the truth. Who let it drift?
SHOW YOUR THINKING
Answer:
Did you know? Rain can take about ten minutes to reach the rainforest floor — the canopy catches it and lets it down leaf by leaf.
4.
You have 12 seed pods that look identical, but one is heavier than the rest. Using a balance scale and no weights, what is the fewest weighings that is guaranteed to find it? Explain your plan.
SHOW YOUR THINKING
Answer:
Did you know? A single hectare of Amazon rainforest can hold more than 300 different tree species — more than some whole countries.
3rd Grade
1. 19 figs.
Work backwards, flipping each step. 11 left after halving → 22 before it. Undo finding 9 → 13. Undo giving 6 away → 19. Check forwards: 19 − 6 = 13, + 9 = 22, half of 22 = 11. ✓
2. 6 birds.
The 6 both-birds got counted twice, so birds with at least one = 13 + 11 − 6 = 18. Then 24 − 18 = 6. Draw two overlapping circles and it goes obvious.
3. 3 minutes — the same as before.
Read it as one monkey and one mango: if 3 monkeys finish 3 mangoes in 3 minutes, then each monkey eats one mango in 3 minutes. Nine monkeys with a mango each still take 3 minutes — they are all eating at once. The trap is multiplying by three.
4. 10 calls.
Each of the 5 calls to the other 4, which is 20 — but that counts every call from both ends, so 20 ÷ 2 = 10. Or add 4 + 3 + 2 + 1.
4th Grade
1. Ibrahim — toucan — Canopy · Khadija — jaguar — Ridge · Sumayya — sloth — River.
Clue 3 gives Khadija the jaguar. Clue 2 then leaves Ibrahim only the toucan, and clue 1 puts the toucan at the Canopy → Ibrahim, Canopy. Sumayya takes the sloth, and clue 4 keeps her off the Ridge → Sumayya, River, so Khadija has the Ridge.
2. Every 56 seconds; 5 times in the first 5 minutes.
Together on the shared multiples of 8 and 14. Multiples of 14 are 14, 28, 42, 56 — and 56 ÷ 8 = 7, so 56 seconds. Five minutes is 300 seconds, and 56, 112, 168, 224, 280 all fit: 5 times (not counting the 6:00:00 start).
3. Harun let it drift.
Test all three. If Umar did it: Umar false, Harun true, Zaynab true — two truths. ✗ If Harun did it: Umar true, Harun false, Zaynab false — exactly one. ✓ If Zaynab did it: Umar true, Harun false, Zaynab true — two. ✗ Only Harun fits.
4. 3 weighings.
Split 4 / 4 / 4. Weigh 1: two of the fours. A sinking side names that four; a balance names the four left out. Weigh 2: split that four 2 / 2 and weigh them. Weigh 3: weigh the last two against each other. 3 every time. Two is not enough: each weighing has only 3 outcomes, and 3 × 3 = 9 is fewer than 12.