Calculating an average in Cambridge pseudocode

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Quick Questions

Shade in the A or B circle for each question.

1. Where should Average ← Total / Count go in a loop that totals marks?

A After the loop has finished (after NEXT)

B Inside the loop, before NEXT

2. Which declaration is best for a variable that stores an average?

A DECLARE Average : INTEGER

B DECLARE Average : REAL

3. Which line correctly calculates the average in Cambridge pseudocode?

A Average ← Total / Count

B Total / Count ← Average

4. Which check stops the program dividing by zero?

A IF Count > 0 THEN

B IF Count = 0 THEN Average ← Total / Count

5. An array Marks has 5 items and the loop adds each one to Total. Which fixed count gives the correct average?

A Average ← Total / Marks

B Average ← Total / 5

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1Average ← Total / Count		AIF Count > 0 THEN Average ← Total / Count ENDIF
2DECLARE Average : REAL		BNEXT Index Average ← Total / Count
3Divide after the loop has finished, so Total holds every value		CAverage is declared as INTEGER, so it cannot store decimal values such as 72.5. It should be declared as REAL.
4Check that Count is above zero before dividing, to avoid dividing by zero		DDivides the finished total by the number of items to give the mean
5FOR Index ← 1 TO 5 Total ← Total + Marks[Index] Average ← Total / Count NEXT Index		ESets up a variable that can store an average with decimal places
6DECLARE Average : INTEGER Average ← Total / Count		FThe average is calculated inside the loop, so it is worked out with an unfinished total. The division should come after NEXT Index.

Definitions

Average ← Total / Count

Fill in the Blanks

Complete each line of code by filling in the missing parts.

DECLARE Average : ____

Average ← Total _ Count

Total ← Total + Scores[Index] ____ Index Average ← Total / Count

IF Count _ 0 THEN Average ← Total / Count ENDIF

DECLARE Marks : ARRAY[1:3] OF INTEGER Total ← Marks[1] + Marks[2] + Marks[3] Average ← Total / _

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A DECLARE Average : REAL

B Total ← 0

C FOR Index = 1 TO 5

D Total ← Total + Marks[Index]

E NEXT Index

F Average ← Total / 5

Question 2

A DECLARE Average : INTEGER

B Total ← 120

C Count ← 8

D Average ← Total / Count

E OUTPUT Average

Question 3

A Count ← 4

B Total ← 1

C FOR Index ← 1 TO Count

D Total ← Total + Marks[Index]

E NEXT Index

F Average ← Total / Count

Question 4

A INPUT Count

B IF Count > 0 THEN

C Average ← Total DIV Count

D ENDIF

Question 5

A DECLARE Average : REAL

B Total ← 75

C Count ← 6

D Total / Count ← Average

E OUTPUT Average

Answer Key

Calculating an average in Cambridge pseudocode

Section A: Quick Questions

A — After the loop has finished (after NEXT)

B — DECLARE Average : REAL

A — Average ← Total / Count

A — IF Count > 0 THEN

B — Average ← Total / 5

Section B: Match the Pairs

Average ← Total / Count → Divides the finished total by the number of items to give the mean

DECLARE Average : REAL → Sets up a variable that can store an average with decimal places

Divide after the loop has finished, so Total holds every value → NEXT Index Average ← Total / Count

Check that Count is above zero before dividing, to avoid dividing by zero → IF Count > 0 THEN Average ← Total / Count ENDIF

FOR Index ← 1 TO 5 Total ← Total + Marks[Index] Average ← Total / Count NEXT Index → The average is calculated inside the loop, so it is worked out with an unfinished total. The division should come after NEXT Index.

DECLARE Average : INTEGER Average ← Total / Count → Average is declared as INTEGER, so it cannot store decimal values such as 72.5. It should be declared as REAL.

Section C: Definitions

Average ← Total / Count — Divides the finished Total by Count after the loop ends, giving the mean. Declare Average as REAL. Check Count > 0 first to avoid dividing by zero.

Section D: Fill in the Blanks

DECLARE Average : REAL

Average ← Total / Count

  Total ← Total + Scores[Index]
NEXT Index
Average ← Total / Count

IF Count > 0 THEN
   Average ← Total / Count
ENDIF

DECLARE Marks : ARRAY[1:3] OF INTEGER
Total ← Marks[1] + Marks[2] + Marks[3]
Average ← Total / 3

Section E: Spot the Error

C — A FOR loop must use ← to set the start value. It should be FOR Index ← 1 TO 5.

A — An average is often a decimal such as 15.5, so Average must be declared as REAL, not INTEGER.

B — Total must start at 0. Starting at 1 adds an extra 1 to the sum, so the average will be wrong. It should be Total ← 0.

C — DIV throws away the decimal part, so the mean would be wrong. Use / to get the exact average: Average ← Total / Count.

D — The variable being assigned to must be on the left of ←. It should be Average ← Total / Count.