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SASMO 2019 Grade 8

Question 1

Scoring for this entire paper: on this platform, start at 0; Q1–15 earn 2 points each and Q16–25 earn 4 points each. Incorrect or blank answers earn 0; maximum 70. Official SASMO rules: start with 15 points; Section A (Q1–15) awards +2/−1/0 for correct/incorrect/blank, and Section B (Q16–25) awards +4/0/0; maximum 85.

In Mathematics, the product of the first $n$ positive integers is written as $n!=n\times(n-1)\times\cdots\times1$. For example, $2!=2\times1$ and $7!=7\times6\times5\times4\times3\times2\times1$. Evaluate:
$$9+(8+7)\times(6!\div5-4-3-2-1).$$
  1. 955
  2. 2019
  3. 2034
  4. 3216
  5. None of the above

Question 2

Which of the following is correct?

Interpret the algebraic statements as identities for all real variables for which both sides are defined.
  1. $(a+b)^3=a^3+b^3$
  2. $-10^2=100$
  3. $\sqrt{x^2+9y^2}=x+3y$
  4. $\frac{x}{x+y}=\frac{x}{x}+\frac{x}{y}$
  5. None of the above

Question 3

The highest common factor (HCF) of two positive integers is 3. If their sum is 21, which could NOT be their least common multiple (LCM)?
  1. 18
  2. 30
  3. 36
  4. 7
  5. None of the above

Question 4

If the five-digit number $5D68D$ is divisible by 36, find the value of the digit $D$.
  1. 0
  2. 2
  3. 4
  4. 8
  5. None of the above

Question 5

If $X=0.0000125$ and $Y=0.00008$, which of the following has the greatest value?
  1. $X+Y$
  2. $X-Y$
  3. $X\times Y$
  4. $X\div Y$
  5. None of the above

Question 6

The price of an ice cream cone in a shop has increased by 20%. How many ice cream cones can now be bought using the amount of money that used to buy 60 such cones?
  1. 50
  2. 48
  3. 40
  4. 56
  5. None of the above

Question 7

The following calculations lead to the conclusion that $\pi>2019$:

(1) Let $x=\pi$ ($3.14159\ldots$), $y=3$ and $z=2019$.

(2) $-x\le -y$ and $z-y>0$.

(3) $x\ge y$ and $z>y$.

(4) Then $x\ge z$.

(5) Therefore, $\pi>2019$.

Which transition is the first that contains an error?
  1. (1) to (2)
  2. (2) to (3)
  3. (3) to (4)
  4. (4) to (5)
  5. None of the above

Question 8

Consider all the integers from 1 to 200. Which statement is NOT true about them?
  1. The sum of all even numbers is greater than the sum of all odd numbers.
  2. Writing all the digits, the digit 0 is the least occurring digit.
  3. The average of the even numbers is greater than the average of the odd numbers.
  4. (Sum of all even numbers) − (Sum of all odd numbers) = 200
  5. The average of the 200 numbers is not a positive integer.

Question 9

Which cube below will be formed when the net is folded?

Question illustration
  1. Cube A in the diagram
  2. Cube B in the diagram
  3. Cube C in the diagram
  4. Cube D in the diagram
  5. Cube E in the diagram

Question 10

How many consecutive zeros are there at the end of $2^{11}\times3^7\times5^5\times7^3\times11^2$?
  1. 11
  2. 16
  3. 6
  4. 5
  5. None of the above

Question 11

The sum of the speeds of two cyclists is 34 km/h. If the first cycles for 3 hours and the second for 7 hours, the total distance travelled is 150 km. Assuming both cycle at constant speeds, what is the difference between their speeds?
  1. 12 km/h
  2. 11 km/h
  3. 10 km/h
  4. 9 km/h
  5. 8 km/h

Question 12

Find $[\sqrt{1+2+3+\cdots+100}]$, where $[x]$ is the greatest integer less than or equal to $x$. For example, $[13.54]=13$.
  1. 69
  2. 70
  3. 71
  4. 72
  5. None of the above

Question 13

Which fraction is the largest?
  1. $\frac{60}{119}$
  2. $\frac{64}{127}$
  3. $\frac{62}{123}$
  4. $\frac{63}{125}$
  5. $\frac{61}{121}$

Question 14

A leader asked his 6 followers what was inside a gift box. They sit around a table. Two truth-tellers sit next to each other, and two liars also sit next to each other. Each of the remaining two followers is either a truth-teller or a liar, and these remaining two do not sit next to each other. Their responses are shown below. What is inside the gift box?

Question illustration

Reading convention: the bottom-right follower has no response printed in the source; leave that response unknown. A truth-teller gives the true object and a liar gives a false object. The adjacent pairs and remaining two are a partition of the six followers.
  1. Camera
  2. Laptop
  3. Wallet
  4. Watch
  5. Insufficient data

Question 15

In the diagram, $ABCD$ is a square with $AB=20$ cm, $AD$ is a diameter of the semicircle, and $AB$ is a radius of the quadrant. Find the area, in cm², of the shaded region.

Question illustration
  1. $75\pi$ cm²
  2. $50\pi$ cm²
  3. $(75\pi-100)$ cm²
  4. $(50\pi-100)$ cm²
  5. None of the above

Question 16

How many triangles are there in the diagram?

Question illustration

Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).

Question 17

The bar chart shows the time Lou spent in the gym last week. The average time of the first 3 days was 72% of the average time of the last 4 days. His total time was 183 minutes. How many minutes did he spend in the gym on Wednesday? Round to the nearest integer.

Question illustration

Chart reading: Monday 21, Tuesday 14 and Saturday 32 minutes are printed values. Other bar heights are schematic and should not be measured as exact data. Monday–Sunday are the seven days in order.

Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).

Question 18

What is the remainder when $2018!+13$ is divided by 2019?

Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).

Question 19

The operator $\otimes$ acts on two numbers as follows:
$$2\otimes6=44,\quad4\otimes10=87,$$
$$8\otimes18=1613,\quad16\otimes22=2019.$$
Find $7\otimes9$.

Pattern convention: finitely many examples do not uniquely define an operator. This source puzzle is graded using the published intended arithmetic-and-digit-concatenation pattern; other rules are mathematically possible.

Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).

Question 20

At a camp, 134 students received a burger and 62 received an ice cream. Fifteen received a burger and an ice cream but no fries, and 31 received all three types of food. There are 200 students. What is the largest possible number who received none of the three types?

Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).