1. GUIDED
A rectangular sample tray has a perimeter of 58 cm. One side measures 11 cm. How long is the other side? What is the area of the tray?
Half the perimeter is one of each side: 58 ÷ 2 =
Take away the side you know: − 11 = cm
Area = 11 × = square cm
Answer:
Did you know? A cut stops bleeding because tiny cell fragments called platelets pile into the gap and turn sticky.
2.
A lab loads 92 blood samples into racks. Each rack holds 6. How many racks are completely full, and how many samples are left over? Then: how many racks are needed to hold every sample?
SHOW YOUR THINKING
Answer:
Did you know? Pus is mostly white blood cells that have finished their work — it is a sign the defence turned up.
3.
A lab grows 146 cultures a day for 8 days. Then 79 of them are found spoiled and thrown out. How many good cultures are left?
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Answer:
Did you know? Your tonsils are lumps of immune tissue placed right at the back of the throat, where swallowed germs go past.
4.
Two dishes sit on the bench. One is 3/5 full. The other is 7/12 full. Which dish holds more? How do you know?
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Answer:
Did you know? Mucus is not waste. It traps dust and germs, and tiny hairs then sweep the whole lot back out.
5.
A rectangular culture plate covers 108 square centimetres. One side measures 12 cm. How long is the other side? What is the perimeter all the way around?
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Answer:
Did you know? A swollen lump in your neck when you are ill is a lymph node at work — it fills with cells fighting the infection.
1. GUIDED
A vial is filled in two goes. In the morning 1/4 of it is filled. In the afternoon another 2/5 is filled. How full is the vial?
A common bottom number for 4 and 5 is
1/4 = /20 and 2/5 = /20
Now add the top numbers only, keep the bottom:
Answer:
Did you know? Your stomach acid is strong enough to kill most germs you swallow before they ever reach the gut.
2.
A store of serum is 7/8 full. Over one week, 1/3 of the store is used. How much serum is left?
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Answer:
Did you know? Blood is a little over half liquid plasma; the red cells, white cells and platelets float in it.
3.
A store room holds 48 trays, and each tray carries 27 slides. How many slides is that altogether?
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Answer:
Did you know? A microlitre of blood — far less than a drop — holds roughly 4,000 to 11,000 white blood cells.
4.
A course of medicine is 9.5 mL in total. A nurse gives 2.4 mL, then later 3.75 mL. How much has been given, and how much is still to come?
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Answer:
Did you know? Bone marrow makes about two million red blood cells every second.
5.
A clinic runs 1,455 tests in 5 days, at a steady rate. At that same rate, how many tests would it run in 9 days? Those results are filed into folders of 8 — how many complete folders is that, and how many results are left over?
SHOW YOUR THINKING
Answer:
Did you know? White blood cells follow a chemical trail to a wound, moving toward wherever the signal is strongest.
3rd Grade
1. Other side 18 cm; area 198 square cm.
Halve the perimeter first: 58 ÷ 2 = 29 — one long side plus one short side. Then 29 − 11 = 18 cm. Area = 11 × 18 = 198 square cm. Answering 47 means the halving was skipped.
2. 15 full racks, 2 left over — but 16 racks to hold them all.
92 ÷ 6 = 15 remainder 2. Those 2 spare samples still need somewhere to sit, so one more rack: 16.
3. 1,089 cultures.
146 × 8 = 1,168, then 1,168 − 79 = 1,089.
4. The 3/5 dish.
Bigger numbers do not mean a bigger fraction. Sixtieths: 3/5 = 36/60, 7/12 = 35/60. 3/5 wins, by one sixtieth.
5. Other side 9 cm; perimeter 42 cm.
Area = side × side, so 108 ÷ 12 = 9 cm. Perimeter goes all the way round: 12 + 9 + 12 + 9 = 42 cm.
4th Grade
1. 13/20 of the vial.
Twentieths: 1/4 = 5/20 and 2/5 = 8/20, so 5/20 + 8/20 = 13/20. Add the tops, keep the bottom.
2. 13/24 of the store.
Twenty-fourths: 7/8 = 21/24 and 1/3 = 8/24. 21/24 − 8/24 = 13/24. The bottom number never changes.
3. 1,296 slides.
48 × 27. Split it: (48 × 20) + (48 × 7) = 960 + 336 = 1,296.
4. 6.15 mL given; 3.35 mL still to come.
Pad to two places, line up the points. 2.40 + 3.75 = 6.15. Then 9.50 − 6.15 = 3.35 mL. Skipped padding gives 6.79.
5. 2,619 tests — 327 complete folders, 3 left over.
Find one day first: 1,455 ÷ 5 = 291 a day. Then 291 × 9 = 2,619. Finally 2,619 ÷ 8 = 327 remainder 3. Check: 2,616 + 3 = 2,619. ✓