1.
A lab grows 115 defender cells in each of 6 dishes. In one battle with a germ, 89 of the cells are used up. How many defender cells are left?
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Answer:
Did you know? White blood cells are your body's defender cells. You make billions of fresh ones every single day.
2.
A team collects 94 blood samples. Each tray holds 8 samples. How many trays are completely full, and how many trays are needed to hold every sample?
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Answer:
Did you know? A single drop of blood holds thousands of defender cells, all patrolling for anything that does not belong.
3.
A ward has 4 rooms with 15 beds each, and 1 more room with 12 beds. How many beds are there altogether?
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Answer:
Did you know? When you rest, your body spends more energy on defence. That is one reason sleep helps you get better faster.
4.
One medicine bottle is 3/4 full. Another is 5/8 full. Which bottle holds more medicine? How do you know?
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Answer:
Did you know? Antibodies are tiny Y-shaped tools your defender cells make, each one built to grab a single kind of germ.
5.
A rectangular lab tray has an area of 72 square cm. One side measures 8 cm. How long is the other side? What is the perimeter of the tray?
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Answer:
Did you know? Once your body beats a germ, it keeps a memory of it. Meet the same germ again and the defence is ready in hours, not days.
1. GUIDED
A test tube is filled in two goes. First 2/5 of it is filled, then 1/3 more. How full is the tube now?
A common bottom number for 5 and 3 is
Rewrite both, then add the tops: 2/5 = /15 + 1/3 = /15 =
Answer:
Did you know? Your bone marrow — the soft centre of your bones — is the factory where most defender cells are born.
2.
A store of vaccine is 7/8 full. Over one week, 1/3 of the full store is used. How much is left?
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Answer:
Did you know? Some defender cells live only a few days; others patrol for years, remembering old battles the whole time.
3.
A lab runs 24 trays, and each tray holds 36 sample wells. How many wells is that altogether?
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Answer:
Did you know? A fever is your body turning up the heat on purpose — many germs breed badly when things get warm.
4.
A vial of serum costs $4.75. A nurse buys 3 vials and pays with a $20 note. How much does she spend, and how much change does she get?
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Answer:
Did you know? The word serum means the clear liquid part of blood — the part that carries antibodies once the cells are removed.
5.
A clinic screens 1,464 people in 6 days, at a steady rate. At that same rate, how many would they screen in 9 days? Those results are filed into folders of 8 — how many complete folders is that, and how many results are left over?
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Answer:
Did you know? Contact tracing during an outbreak is a giant sorting job — thousands of records filed, checked, and followed up one by one.
3rd Grade
1. 601 defender cells left.
115 × 6 = 690, then 690 − 89 = 601. Multiply first, subtract second.
2. 11 full trays, 6 left over — but 12 trays to hold them all.
94 ÷ 8 = 11 remainder 6. The 6 spares still need a tray, so 12. "11" is one step short.
3. 72 beds.
4 × 15 = 60, then 60 + 12 = 72. Multiply first, then add the last room.
4. The 3/4 bottle.
Eighths: 3/4 = 6/8 vs 5/8, so 3/4 holds more — but only once the eighths make them fair to compare.
5. Other side 9 cm; perimeter 34 cm.
72 ÷ 8 = 9 cm (the missing side). Perimeter = 2 × (8 + 9) = 34 cm. Gives area, asks perimeter — reverse of yesterday.
4th Grade
1. 11/15 of the tube.
Fifteenths: 2/5 = 6/15, 1/3 = 5/15, so 6/15 + 5/15 = 11/15. Both had to change — neither was already 15.
2. 13/24 of the store.
Twenty-fourths: 7/8 = 21/24, 1/3 = 8/24. 21/24 − 8/24 = 13/24. No scaffold, and a subtraction.
3. 864 wells.
24 × 36 = (24 × 30) + (24 × 6) = 720 + 144 = 864.
4. $14.25 spent; $5.75 change.
4.75 × 3 = 14.25, then 20.00 − 14.25 = 5.75. Pad the 20 as 20.00 and line up the points.
5. 2,196 people — 274 complete folders, 4 left over.
Day first: 1,464 ÷ 6 = 244. Then 244 × 9 = 2,196. Then 2,196 ÷ 8 = 274 r 4. Check: 274 × 8 + 4 = 2,196. ✓