30 questions with worked solutions. Both papers: applied mathematical knowledge, and logic and proof, including contrapositives, counterexamples and necessary and sufficient conditions.
10 easy · 18 medium · 2 hard · TMUA Paper 2 · TMUA Paper 1
What is the contrapositive of the statement "if n2 is even, then n is even"?
If n is even, then n2 is even.
If n2 is odd, then n is odd.
If n is odd, then n2 is odd.
If n is odd, then n2 is even.
n2 is even and n is odd.
Show answer
Answer: C. If n is odd, then n2 is odd.
The contrapositive of "P⇒Q" is "not Q⇒ not P": if n is not even, then n2 is not even. The first option is the converse, the second the inverse, and the last is the negation.
2EasyTMUA Paper 2
Which value of x is a counterexample to the claim "for all real x, if x2>4 then x>2"?
x=3
x=−3
x=2
x=0
x=−2
Show answer
Answer: B. x=−3
A counterexample makes the hypothesis true and the conclusion false. x=−3: x2=9>4 but x<2. For x=−2 the hypothesis fails (4>4).
3EasyTMUA Paper 2
For real x, the condition x>1 is which of the following for x2>1?
Necessary but not sufficient
Necessary and sufficient
Neither necessary nor sufficient
Sufficient but not necessary
Show answer
Answer: D. Sufficient but not necessary
If x>1 then x2>1, so it is sufficient. But x=−2 has x2>1 without x>1, so it is not necessary.
4MediumTMUA Paper 2
What is the negation of "every student passed at least one exam"?
Every student failed at least one exam.
No student passed any exam.
Some student failed at least one exam.
Some student passed no exam.
Every student failed every exam.
Show answer
Answer: D. Some student passed no exam.
Negating "for all s, there exists an exam e that s passed" gives "there exists s such that for all e, s did not pass e": some student passed no exam.
5EasyTMUA Paper 1
How many real solutions does 32x−4⋅3x+3=0 have?
0
1
2
3
4
Show answer
Answer: C. 2
Put y=3x>0: y2−4y+3=0, so y=1 or y=3, giving x=0 or x=1.
6MediumTMUA Paper 1
∫14xx+2dx=
320
8
326
328
10
Show answer
Answer: C. 326
Split: x1/2+2x−1/2, integrating to 32x3/2+4x1/2. At 4: 316+8=340. At 1: 32+4=314. Difference 326.
7MediumTMUA Paper 1
What is the sum of all real solutions of log2x+log2(x−2)=3?
−2
2
4
6
8
Show answer
Answer: C. 4
x(x−2)=8 gives x=4 or x=−2. But log2x needs x>0 (and x−2>0), so only x=4 is a solution. The sum of the quadratic's roots, 2, is the trap.
8EasyTMUA Paper 1
What is the minimum value of xx2+4 for x>0?
1
2
3
4
There is no minimum
Show answer
Answer: D. 4
x+x4≥2x⋅x4=4 by AM–GM, with equality at x=2.
9MediumTMUA Paper 2
A "proof" that 1=2: Let a=b. (Step 1) a2=ab. (Step 2) a2−b2=ab−b2. (Step 3) (a+b)(a−b)=b(a−b). (Step 4) a+b=b. (Step 5) 2b=b. (Step 6) 2=1. Which is the first incorrect step?
Step 2
Step 3
Step 4
Step 5
Step 6
Show answer
Answer: C. Step 4
Step 4 divides both sides by a−b, which is 0 since a=b. Steps 1 to 3 are valid identities. Step 6 would also be invalid if b=0, but the first error is Step 4.
10MediumTMUA Paper 1
For how many integers n is n−312 an integer?
6
8
11
12
24
Show answer
Answer: D. 12
n−3 must divide 12, and it may be negative: ±1,±2,±3,±4,±6,±12. That is 12 values of n.
11MediumTMUA Paper 1
For 0≤θ≤π, the series k=0∑∞(2cosθ)k converges exactly when
0<θ<3π
6π<θ<65π
3π<θ<32π
2π<θ<π
0≤θ≤π
Show answer
Answer: C. 3π<θ<32π
A geometric series converges iff ∣2cosθ∣<1, i.e. −21<cosθ<21. On [0,π] that is 3π<θ<32π.
12EasyTMUA Paper 1
What is the area of the triangle with vertices (0,0), (4,1) and (1,3)?
29
5
211
6
213
Show answer
Answer: C. 211
With one vertex at the origin, area =21∣x1y2−x2y1∣=21∣4⋅3−1⋅1∣=211.
13MediumTMUA Paper 1
If f(x)=2x+1 and g(x)=x2, how many real x satisfy f(g(x))=g(f(x))?
0
1
2
3
4
Show answer
Answer: C. 2
2x2+1=(2x+1)2=4x2+4x+1, so 2x2+4x=0 and x=0 or x=−2.
14MediumTMUA Paper 1
k=1∑10log10(kk+1)=
1
log1011
log10(10!)
10
11
Show answer
Answer: B. log1011
The sum of logs is the log of the product, and ∏k=110kk+1=111 telescopes.
15MediumTMUA Paper 2
Which of these statements are true for every real x? I: x2+1≥2x. II: x3≥x. III: ∣x∣≥x.
I only
II only
III only
I and III only
I, II and III
Show answer
Answer: D. I and III only
I is (x−1)2≥0: true. II fails at x=−2 (−8<−2). III is true because ∣x∣ is x or −x≥0>x. So I and III only.
16EasyTMUA Paper 1
What is the gradient of y=x3−3x at the point where it crosses the positive x-axis?
0
3
33
6
9
Show answer
Answer: D. 6
x3−3x=x(x2−3) is zero at x=3 on the positive axis. y′=3x2−3=9−3=6.
17MediumTMUA Paper 1
How many integers n with 1≤n≤50 have no common factor with 50 other than 1?
10
16
20
25
40
Show answer
Answer: C. 20
Exclude multiples of 2 or 5: 50−25−10+5=20. This is Euler's φ(50)=50⋅21⋅54.
18MediumTMUA Paper 2
The claim "for every integer n≥0, n2+n+41 is prime" is false. Which value of n is a counterexample?
n=1
n=10
n=39
n=40
There is none
Show answer
Answer: D. n=40
At n=40: 1600+40+41=1681=412. (The polynomial gives primes for n=0,…,39; at n=39 it is 1601, which is prime.) The factorisation is easy to see by writing 402+40+41=40⋅41+41=412.
19MediumTMUA Paper 1
The curve y=xe−x has exactly one stationary point. What is it?
(0,0), a minimum
(1,e1), a minimum
(1,e1), a maximum
(−1,−e), a maximum
(e,1), a maximum
Show answer
Answer: C. (1,e1), a maximum
y′=(1−x)e−x vanishes at x=1, where y=e−1. y′ changes from positive to negative there, so it is a maximum.
20HardTMUA Paper 2
Consider the statement "if n is prime, then 2n−1 is prime" and its converse. Which is correct?
Both are true.
Both are false.
The statement is true and its converse is false.
The statement is false and its converse is true.
Show answer
Answer: D. The statement is false and its converse is true.
The statement fails at n=11: 211−1=2047=23⋅89. The converse holds: if n=ab with a,b>1, then 2a−1 divides 2ab−1, so 2n−1 is composite.
21MediumTMUA Paper 2
Which statement is logically equivalent to "P only if Q"?
Q⇒P
P⇒Q
P⇔Q
(not P) ⇒ (not Q)
Q only if P
Show answer
Answer: B. P⇒Q
"P only if Q" says P cannot hold without Q, which is P⇒Q. "P if Q" is the other direction.
22MediumTMUA Paper 1
How many real solutions does x4+x2−2=0 have?
0
1
2
3
4
Show answer
Answer: C. 2
With y=x2: y2+y−2=0, so y=1 or y=−2. Only y=1 is possible for real x, giving x=±1.
23MediumTMUA Paper 1
What is the sum of the coefficients of (2x−3)5?
−243
−1
1
32
243
Show answer
Answer: B. −1
The sum of the coefficients is the value at x=1: (2−3)5=−1.
24EasyTMUA Paper 1
If tanθ=43 and θ is acute, what is sinθ+cosθ?
1
57
45
512
47
Show answer
Answer: B. 57
The 3-4-5 triangle gives sinθ=53 and cosθ=54.
25MediumTMUA Paper 2
Which of these statements is false?
Every prime greater than 2 is odd.
If n2 is divisible by 4 then n is divisible by 4.
The sum of two odd integers is even.
Every integer is rational.
There are infinitely many primes.
Show answer
Answer: B. If n2 is divisible by 4 then n is divisible by 4.
Take n=2: n2=4 is divisible by 4 but n is not. The correct statement is that n must be even.
26EasyTMUA Paper 1
What is the remainder when x3−2x+5 is divided by x−2?
5
7
9
11
13
Show answer
Answer: C. 9
By the remainder theorem, substitute x=2: 8−4+5=9.
27MediumTMUA Paper 1
The quadratic x2+bx+9 has a repeated root. What is the sum of the possible values of b?
−6
0
6
12
36
Show answer
Answer: B. 0
b2=36, so b=±6 and the two values cancel.
28HardTMUA Paper 2
A "proof" by induction claims that in any set of n horses all the horses have the same colour. The base case n=1 is fine, and the inductive step removes one horse, applies the hypothesis, and puts it back. Where does the argument fail?
The base case
The step from n=1 to n=2
The step from n=2 to n=3
The inductive hypothesis is not stated
It does not fail
Show answer
Answer: B. The step from n=1 to n=2
The step needs the two smaller sets to overlap. For n=2 they do not, so nothing forces the two horses to match. Every later step is fine, which is why the flaw is easy to miss.
29EasyTMUA Paper 1
How many integers x satisfy 2<3x−4<20?
4
5
6
7
8
Show answer
Answer: B. 5
6<3x<24, so 2<x<8: the integers 3, 4, 5, 6, 7.
30MediumTMUA Paper 2
The claim "for all real x and y, if x2=y2 then x=y" is false. Which single change makes it true?
Replace = in the conclusion by ≥
Add the condition x>0 and y>0
Replace x2=y2 by x3=y3
Either of the second or third changes
None of these changes works
Show answer
Answer: D. Either of the second or third changes
Restricting to positives removes the case x=−y, and cubing is one-to-one on the reals, so either change repairs it.