The order of brackets, indices (square and cube roots) and operations
Work out
7 × (3 + 2)
- 42
- 23
- 35
- 12
Show the answer
35. Brackets first: 3 + 2 = 5, then 7 × 5 = 35.
Huh Lab Maths › Cambridge Lower Secondary Maths › Stage 8
Stage 8 of the Cambridge Lower Secondary Mathematics (0862) curriculum framework, usually Year 8 (ages 12 to 13). Here is what each part asks, a practice question for each, and the mistakes that cost the most marks.
Each part with one practice question, made by the same engine your child plays.
Work out
7 × (3 + 2)
35. Brackets first: 3 + 2 = 5, then 7 × 5 = 35.
−30 ÷ (−6) = ?
5. 30 ÷ 6 = 5. The signs are the same, so the answer is positive. 5.
Write 12 as a product of prime factors.
2² × 3. Keep dividing by primes: 12 = 2² × 3.
Which of these is a natural number?
1. Natural numbers are 1, 2, 3, … ; integers add 0 and the negatives; rational numbers are any fraction of integers, so they add decimals like 2.5 and fractions like 1/2.
Simplify x⁹ × x³
x¹². Multiplying: add the powers. 9 + 3 = 12.
Which numbers, squared, give 9?
3 and −3. 3² = 9 and (−3)² = 9 too. Every positive number has two square roots.
What is ∛(−216)?
−6. (−6) × (−6) × (−6) = −216: three negatives multiply to a negative. So ∛(−216) = −6. (A square root of a negative has no real answer, but a cube root does.)
6 ÷ 0.01 = ?
600. Dividing by 0.01 makes a number BIGGER: it is the same as multiplying by 100. 600.
Round 0.02276 to 3 significant figures.
0.0228. The zeros at the front only hold the place: they are not significant. Count 3 digits from the first non-zero one: 0.0228.
Which fraction is equal to a RECURRING decimal?
5/12. 5/12 = 0.4167…, and the digits go on repeating. The others stop.
5 5/6 − 3 1/6 = ?
(simplest form)
2 2/3. Wholes: 5 − 3 = 2. Fractions: 5/6 − 1/6 = 2/3. Together 2 2/3.
1/6 ÷ 1/7 = ?
7/6. Flip the second fraction and multiply: 1/6 × 7/1 = 7/6.
Which is the same as 7 × (24 + 4)?
7 × 24 + 7 × 4. Multiplying a bracket multiplies EVERYTHING inside it: 7 × 24 + 7 × 4 = 168 + 28 = 196.
Decrease $60 by 10%.
$54. 10% of 60 is 6. 60 − 6 = 54.
Which is the SMALLEST?
⅖ 0.3 −1.2 −0.5
−1.2. As decimals: ⅖ = 0.4, 0.3 = 0.3, −1.2 = −1.2, −0.5 = −0.5. On a number line the smallest is the one furthest left: −1.2. Below zero, a bigger number AFTER the minus sign is SMALLER.
0.9 × 0.3 = ?
0.27. Multiply as whole numbers: 9 × 3 = 27. Count the decimal places in the question (1 + 1) and put that many back: 0.27.
0.9 ÷ 0.3 = ?
3. Multiply both numbers by 10 so the divisor is whole: 9 ÷ 3 = 3. The answer is bigger than the number you started with, because you are dividing by less than 1.
Boys and girls in a club are in the ratio 4:3.
What PROPORTION of the club are boys?
4/7. 4:3 means 4 boys in every 7 children, so the proportion of boys is 4/7.
Write the ratio 15 minutes : 2 hours in its simplest form.
1 : 8. Make the units the same first: 2 hours = 120 minutes. Then 15 : 120 = 1 : 8.
$170 is shared in the ratio 2 : 3.
How much is the smaller share?
$68. 2 + 3 = 5 parts. One part is 170 ÷ 5 = 34. The smaller share is 2 × 34 = 68.
Which of these is an EQUATION, where the letter is an unknown to be found?
3x + 2 = 11. 3x + 2 = 11: where the letter is an unknown to be found.
Which is the same as x × 6 × y?
6xy. Multiplication can be done in any order (commutative): x × 5 × y = 5xy.
Factorise fully
8y + 28
4(2y + 7). The highest common factor of 8y and 28 is 4. Take it outside: 4(2y + 7).
A third of a number t, and then 9 is taken away.
Which expression is this?
t/3 − 9. A third of t is t/3. Then take 9 away from it: t/3 − 9.
A phone plan costs $40 a month plus $45 for every gigabyte used.
h is the number of gigabytes and C is the bill in dollars.
Which formula is right?
C = 45h + 40. Every one of the gigabytes adds 45, which is 45h. The 40 is paid once, whatever h is: C = 45h + 40.
Ben has 8 full boxes of pens and 6 loose pens.
Tom has 2 full boxes and 60 loose pens.
They have the SAME number of pens. How many pens are in a full box?
9. The equation is 8n + 6 = 2n + 60. Take 2n from both sides: 6n + 6 = 60. So 6n = 54 and n = 9.
Solve
3x − 3 > −6
x > −1. Add 3, then divide by 3. The sign stays the same.
A sequence starts at 2 and the rule is "add 2/3".
What is the 4th term?
4. 2, 8/3, 10/3, 4: three steps of 2/3 from the start.
Find the nth term.
4, 13, 22, 31, …
9n − 5. It goes up in 9s, so it starts 9n. When n = 1, 9n = 9, and the first term is 4: adjust by −5.
A function machine: input → × 3 → + 4 → output.
The INPUT is 8. What comes out?
28. 8 × 3 = 24, then + 4 = 28.
A phone plan costs $27 a month plus $35 for every gigabyte used.
x is the number of gigabytes and y is the bill in dollars.
Which equation is right?
y = 35x + 27. Every one of the gigabytes adds 35, which is 35x. The 27 is paid once, whatever x is: y = 35x + 27.
A point on the line y = 2x − 3 has x = −1.
What are its coordinates?
(−1, −5). Put x = −1 into the equation: y = −5. The point is (−1, −5): x first, then y.
What is the gradient of
y = x + 6?
1. In y = mx + c the gradient is m, the number in front of x: 1.
Gym A costs $30 to join plus $4 a visit. Gym B costs $5 a visit.
Their cost graphs cross at 30 visits. What does the crossing mean?
At 30 visits both gyms cost the same. Where two cost lines cross, the costs are EQUAL: 30 + 4 × 30 = 5 × 30 = $150. After that the lines swap: Gym A (the flatter line) becomes cheaper.
Which quadrilateral has two pairs of equal sides next to each other, and no parallel sides?
kite. That describes a kite.
A circle has diameter 12 cm.
Find its circumference, in terms of π.
12π cm. Circumference = 2πr = 2 × π × 6 = 12π cm.
5 miles is about 8 km.
About how many km is 5 miles?
8 km. 5 ÷ 5 = 1 lots of 5 miles, each about 8 km: 1 × 8 = 8 km.
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
A solid has 8 faces and 18 edges.
Use Euler's formula to find how many vertices it has.
12. Faces + vertices − edges = 2 for every solid like this: 8 + 12 − 18 = 2. So vertices = 18 − 8 + 2 = 12.
A prism has a triangular cross-section with
base 6 cm and height 7 cm. It is 3 cm long.
Find its volume.
63 cm³. Cross-section = ½ × 6 × 7 = 21 cm². Times length 3 = 63 cm³.
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
A square-based pyramid has base edges of 8 cm.
Each triangular face has a slant height of 9 cm.
Find its total surface area.
208 cm². Base: 8 × 8 = 64. Four triangles, each ½ × 8 × 9 = 36: 4 × 36 = 144. Total 208 cm².
A regular polygon has rotational symmetry of order 10.
How many sides does it have?
10. A regular polygon with n sides has n lines of symmetry and rotational symmetry of order n. Here n = 10.
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
Two parallel lines are crossed by a third line.
One angle is 70°. What is its alternate angle?
70°. Alternate angles (the Z shape) are equal: 70°.
The bearing of B from A is 265°.
What is the bearing of A from B?
085°. Turn round: add 180° if the bearing is under 180°, take 180° away if it is over. 265° − 180° = 085°.
Find the midpoint of
(−4, 3) and (2, 11).
(−1, 7). Average the x values and the y values: (−1, 7).
a = (5, 1) b = (5, −1)
Find a + b.
(10, 0). Add the x parts and the y parts: (5 + 5, 1 + −1).
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
The point (−6, −4) is enlarged with centre (0, 0)
and scale factor 2. Where does it go?
(−12, −8). From the origin, multiply BOTH coordinates by 2: (−12, −8).
50 pupils are chosen so that each year group has the same share of the sample as it has of the school.
Which sampling method is this?
stratified. 50 pupils are chosen so that each year group has the same share of the sample as it has of the school. That is stratified sampling: every group is represented in the right proportion.
Score: 1, 2, 3, 4
Frequency: 2, 2, 4, 6
Find the mean score.
3. Total of score × frequency = 42. Total frequency = 14. 42 ÷ 14 = 3.
Test scores.
Class A: mean 61, range 15.
Class B: mean 64, range 8.
Which class did better on average?
Class B. "On average" means compare the means: 64 is higher, so Class B. The range says nothing about how high the scores were.
The questions for this part come with a picture or are played as a game, so they are best tried in Huh Lab.
The probability that it rains is 0.45.
What is the probability that it does not rain?
0.55. 1 − 0.45 = 0.55.
Two fair coins are tossed.
How many possible outcomes are there?
4. List them: HH, HT, TH, TT. Four, and they are equally likely.
Two fair coins are tossed.
What is the probability of one head and one tail?
1/2. The four equally likely outcomes are HH, HT, TH, TT. One head and one tail happens in 2 of them: 1/2.
Huh Lab checks every wrong answer against known mistakes like these, and goes back to the step behind the one your child keeps making.
Whatever is done to x must be UNDONE on the other side: + becomes −, × becomes ÷.
Use a number line: below zero the numbers keep counting, in the other direction.
Along the corridor, THEN up the stairs: x comes before y.
Dividing by 0.5 asks "how many halves fit?", so the answer gets BIGGER.
Ask "what happens to the number FIRST?" Whatever happens first stays together, in brackets if it needs them.
Multiply and divide before adding and subtracting.
Count the faces before adding: a cuboid has 6, a closed cylinder has two circles and the curved part.
Estimate first: 3.45 × 6 is about 3 × 6 = 18, so the answer is near 20.
Short rounds on any topic, a new question every time, the exact mistake found, and a report to you after every session.
15 extra days free with your first month · Up to 5 children · 30-day money-back guarantee