Secondary 3 Additional Mathematics Numbers Ratio Proportion Quiz

Secondary 3 Additional Mathematics Quiz - Numbers Ratio Proportion (Answer Key)

1. Simplify $\sqrt{75} - 2\sqrt{12} + \sqrt{48}$
$\sqrt{75} = \sqrt{25 \times 3} = 5\sqrt{3}$
$2\sqrt{12} = 2\sqrt{4 \times 3} = 2(2\sqrt{3}) = 4\sqrt{3}$
$\sqrt{48} = \sqrt{16 \times 3} = 4\sqrt{3}$
Expression $= 5\sqrt{3} - 4\sqrt{3} + 4\sqrt{3} = 5\sqrt{3}$
Answer: $5\sqrt{3}$
[2 marks: 1 for simplifying at least two terms correctly, 1 for final answer]

2. Expand $(3\sqrt{2} - \sqrt{5})(2\sqrt{2} + 3\sqrt{5})$
$= 3\sqrt{2}(2\sqrt{2}) + 3\sqrt{2}(3\sqrt{5}) - \sqrt{5}(2\sqrt{2}) - \sqrt{5}(3\sqrt{5})$
$= 6(2) + 9\sqrt{10} - 2\sqrt{10} - 3(5)$
$= 12 + 7\sqrt{10} - 15$
$= 7\sqrt{10} - 3$
Answer: $7\sqrt{10} - 3$
[3 marks: 1 for expansion, 1 for simplifying surds/integers, 1 for final answer]

3. Rationalise $\frac{6}{\sqrt{12} - \sqrt{3}}$
First simplify denominator: $\sqrt{12} - \sqrt{3} = 2\sqrt{3} - \sqrt{3} = \sqrt{3}$
Expression becomes $\frac{6}{\sqrt{3}}$
Rationalise: $\frac{6\sqrt{3}}{3} = 2\sqrt{3}$
Answer: $2\sqrt{3}$
[3 marks: 1 for simplifying denominator, 1 for rationalisation step, 1 for final answer]

4. Given $x = \sqrt{3} + 1, y = \sqrt{3} - 1$, find $x^2 + y^2$
$x^2 = (\sqrt{3} + 1)^2 = 3 + 2\sqrt{3} + 1 = 4 + 2\sqrt{3}$
$y^2 = (\sqrt{3} - 1)^2 = 3 - 2\sqrt{3} + 1 = 4 - 2\sqrt{3}$
$x^2 + y^2 = (4 + 2\sqrt{3}) + (4 - 2\sqrt{3}) = 8$
Answer: 8
[2 marks: 1 for correct expansion of squares, 1 for final sum]

5. Show that $\frac{1}{\sqrt{5} + 2} + \frac{1}{\sqrt{5} - 2} = 2\sqrt{5}$
LHS $= \frac{1(\sqrt{5}-2)}{(\sqrt{5}+2)(\sqrt{5}-2)} + \frac{1(\sqrt{5}+2)}{(\sqrt{5}-2)(\sqrt{5}+2)}$
Denominator $= 5 - 4 = 1$
LHS $= (\sqrt{5} - 2) + (\sqrt{5} + 2)$
$= 2\sqrt{5}$
$= \text{RHS}$
[4 marks: 1 for correct conjugates, 1 for common denominator, 1 for numerator simplification, 1 for final conclusion]

6. Solve $2^{2x+1} = 32$
$32 = 2^5$
$2x + 1 = 5$
$2x = 4$
$x = 2$
Answer: $x = 2$
[2 marks: 1 for equating indices, 1 for solution]

7. Solve $3^{x^2 - 2x} = \frac{1}{27}$
$\frac{1}{27} = 3^{-3}$
$x^2 - 2x = -3$
$x^2 - 2x + 3 = 0$
Discriminant $\Delta = (-2)^2 - 4(1)(3) = 4 - 12 = -8 < 0$
No real solutions.
Answer: No real solution
[3 marks: 1 for converting RHS, 1 for quadratic equation, 1 for identifying no real roots]

8. Given $4^x = 8^{y+1}$, express $x$ in terms of $y$
$(2^2)^x = (2^3)^{y+1}$
$2^{2x} = 2^{3(y+1)}$
$2x = 3(y+1)$
$2x = 3y + 3$
$x = \frac{3y + 3}{2}$
Answer: $x = \frac{3y + 3}{2}$
[3 marks: 1 for base conversion, 1 for equating indices, 1 for final expression]

9. Solve $\sqrt{2x + 3} = x$
Square both sides: $2x + 3 = x^2$
$x^2 - 2x - 3 = 0$
$(x - 3)(x + 1) = 0$
$x = 3$ or $x = -1$
Check: If $x = -1$, LHS $= \sqrt{1} = 1$, RHS $= -1$. $1 \neq -1$ (Reject)
If $x = 3$, LHS $= \sqrt{9} = 3$, RHS $= 3$. (Accept)
Answer: $x = 3$
[3 marks: 1 for solving quadratic, 1 for checking validity, 1 for final answer]

10. Solve $\sqrt{x + 5} - \sqrt{x} = 1$
$\sqrt{x + 5} = 1 + \sqrt{x}$
Square both sides: $x + 5 = 1 + 2\sqrt{x} + x$
$5 = 1 + 2\sqrt{x}$
$4 = 2\sqrt{x}$
$2 = \sqrt{x}$
Square again: $x = 4$
Check: $\sqrt{9} - \sqrt{4} = 3 - 2 = 1$. (Valid)
Answer: $x = 4$
[3 marks: 1 for isolation and squaring, 1 for solving for $\sqrt{x}$, 1 for final answer]

11. $y$ varies directly as $x^2$. $x=3, y=45$.
(a) $y = kx^2$
$45 = k(3^2) \Rightarrow 45 = 9k \Rightarrow k = 5$
Equation: $y = 5x^2$
(b) When $x = 5$:
$y = 5(5^2) = 5(25) = 125$
Answer: (a) $y = 5x^2$, (b) 125
[3 marks: 1 for k, 1 for equation, 1 for final value]

12. $p$ varies inversely as $\sqrt[3]{q}$. $q=8, p=5$.
(a) $p = \frac{k}{\sqrt[3]{q}}$
$5 = \frac{k}{\sqrt[3]{8}} \Rightarrow 5 = \frac{k}{2} \Rightarrow k = 10$
Equation: $p = \frac{10}{\sqrt[3]{q}}$
(b) When $p = 10$:
$10 = \frac{10}{\sqrt[3]{q}} \Rightarrow \sqrt[3]{q} = 1 \Rightarrow q = 1^3 = 1$
Answer: (a) $p = \frac{10}{\sqrt[3]{q}}$, (b) 1
[4 marks: 1 for k, 1 for equation, 1 for substitution, 1 for final value]

13. $z = k \frac{x^2}{y}$. $z=12, x=4, y=2$.
(a) $12 = k \frac{4^2}{2} = k \frac{16}{2} = 8k \Rightarrow k = 1.5$
(b) New $x = 1.1x$, New $y = 0.9y$
New $z = 1.5 \frac{(1.1x)^2}{0.9y} = 1.5 \frac{1.21 x^2}{0.9 y} = \frac{1.21}{0.9} \left( 1.5 \frac{x^2}{y} \right)$
New $z = \frac{1.21}{0.9} z_{old} = 1.3444... z_{old}$
Percentage change $= (1.3444... - 1) \times 100\% = 34.4\%$ increase.
Answer: (a) $k=1.5$, (b) 34.4% increase
[5 marks: 1 for k, 1 for setting up new ratio, 1 for calculation factor, 1 for percentage conversion, 1 for "increase"]

14. $R \propto \frac{L}{d^2} \Rightarrow R = \frac{kL}{d^2}$.
$L=100, d=2, R=5$.
(a) $5 = \frac{k(100)}{2^2} = \frac{100k}{4} = 25k \Rightarrow k = 0.2$
Formula: $R = \frac{0.2L}{d^2}$
(b) $L=150, d=3$.
$R = \frac{0.2(150)}{3^2} = \frac{30}{9} = \frac{10}{3} = 3.33 \, \Omega$
Answer: (a) $R = \frac{0.2L}{d^2}$, (b) $3.33 \, \Omega$
[3 marks: 1 for formula/constants, 1 for substitution, 1 for final answer]

15. $T = k_1 D + k_2 D^2$.
$D=10, T=25 \Rightarrow 25 = 10k_1 + 100k_2$ (Eq 1)
$D=20, T=70 \Rightarrow 70 = 20k_1 + 400k_2$ (Eq 2)
Divide Eq 2 by 10: $7 = 2k_1 + 40k_2$
From Eq 1: $2.5 = k_1 + 10k_2 \Rightarrow k_1 = 2.5 - 10k_2$
Sub into modified Eq 2: $7 = 2(2.5 - 10k_2) + 40k_2$
$7 = 5 - 20k_2 + 40k_2$
$2 = 20k_2 \Rightarrow k_2 = 0.1$
$k_1 = 2.5 - 10(0.1) = 1.5$
(a) $T = 1.5D + 0.1D^2$
(b) $D=30$: $T = 1.5(30) + 0.1(30^2) = 45 + 0.1(900) = 45 + 90 = 135$ minutes.
Answer: (a) $T = 1.5D + 0.1D^2$, (b) 135 minutes
[4 marks: 1 for setting up equations, 1 for solving constants, 1 for equation, 1 for final calculation]

16. $A = k B C^2$.
$24 = k(3)(2^2) = 12k \Rightarrow k = 2$.
Formula: $A = 2BC^2$.
When $B=5, C=3$:
$A = 2(5)(3^2) = 10(9) = 90$.
Answer: 90
[3 marks: 1 for k, 1 for formula, 1 for final answer]

17. $C = a + bn$.
$500 = a + 100b$ (1)
$900 = a + 200b$ (2)
(2) - (1): $400 = 100b \Rightarrow b = 4$.
$a = 500 - 100(4) = 100$.
(a) $C = 100 + 4n$
(b) $n=150 \Rightarrow C = 100 + 4(150) = 100 + 600 = 700$.
Answer: (a) $C = 100 + 4n$, (b) $700
[3 marks: 1 for constants, 1 for formula, 1 for final calculation]

18. $y = \frac{k}{\sqrt{x}}$.
$10 = \frac{k}{\sqrt{4}} = \frac{k}{2} \Rightarrow k = 20$.
Equation: $y = \frac{20}{\sqrt{x}}$.
When $y=5$: $5 = \frac{20}{\sqrt{x}} \Rightarrow \sqrt{x} = 4 \Rightarrow x = 16$.
Answer: 16
[2 marks: 1 for constant/equation, 1 for final answer]

19. $V = \frac{kT}{P}$.
$200 = \frac{k(300)}{100} = 3k \Rightarrow k = \frac{200}{3}$.
New V: $V = \frac{\frac{200}{3}(350)}{140} = \frac{200 \times 350}{3 \times 140}$.
$350/140 = 2.5 = 5/2$.
$V = \frac{200 \times 5}{3 \times 2} = \frac{1000}{6} = 166.66...$
Answer: 167 cm$^3$ (3 s.f.)
[3 marks: 1 for constant, 1 for substitution, 1 for final answer]

20. Simplify $\frac{\sqrt{18} + \sqrt{8}}{\sqrt{2}}$
$\sqrt{18} = 3\sqrt{2}$, $\sqrt{8} = 2\sqrt{2}$.
Numerator $= 3\sqrt{2} + 2\sqrt{2} = 5\sqrt{2}$.
Expression $= \frac{5\sqrt{2}}{\sqrt{2}} = 5$.
Answer: 5
[2 marks: 1 for simplifying surds, 1 for final division]