Most and least significant bit

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Quick Questions

Shade in the A or B circle for each question.

1. In the binary number 1001, which bit is the most significant bit (MSB)?

A The rightmost 1

B The leftmost 1

2. In the binary number 0110, which bit is the least significant bit (LSB)?

A The leftmost 0

B The rightmost 0

3. Which statement is true for the 8-bit number 10000000?

A The leftmost bit is worth 128

B The leftmost bit is worth 1

4. Where do you start when you work out place values (1, 2, 4, 8...) of a binary number?

A From the right, with the smallest place value 1

B From the left, with the smallest place value 1

5. Why does changing the leftmost bit of 1000 change the number the most?

A It has the biggest place value

B It is the first bit you type

Match the Pairs

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

Left column		Right column
11000		A0101 -> 1101
20111		BThe most significant bit is the leftmost bit, not the rightmost. In 0110 it is the 0 on the left.
3Flipping the leftmost bit of 0101 changes the number the most, because it has the biggest place value		COdd or even depends on the rightmost bit, not the leftmost. 1100 ends in 0, so it is even (12).
4The rightmost bit decides odd or even: 0 means the number is even		D1010 = 10 (even)
5The most significant bit of 0110 is the 0 on the right.		EThe rightmost bit is 1, so it is the least significant bit. It is worth 1 and tells us the number is odd.
61100 is odd because it starts with 1.		FThe leftmost bit is 1, so it is the most significant bit. It is worth 8 and makes this number big.

Definitions

most significant bit

Fill in the Blanks

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

Leftmost bit = ____ significant bit (MSB)

Rightmost bit = _____ significant bit (LSB)

In 8-bit binary, the left bit is worth ___

10111 ends in 1, so the number is ___

Place values from the right: 1, 2, 4, 8, __

Spot the Error

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

Question 1

A number = 1011

B MSB = leftmost bit

C LSB = rightmost bit

D LSB is 1, so number is even

Question 2

A number = 10000

B MSB place value = 1

C LSB place value = 1

Question 3

A number = 0110

B LSB = 0, so number is odd

C MSB = 0

Question 4

A binary = 1000

B MSB = 1

C LSB = 1

D value = 8

Question 5

A start = 0101

B flip the MSB to get 1101

C number changes by 1

Answer Key

Most and least significant bit

Section A: Quick Questions

B — The leftmost 1

B — The rightmost 0

A — The leftmost bit is worth 128

A — From the right, with the smallest place value 1

A — It has the biggest place value

Section B: Match the Pairs

1000 → The leftmost bit is 1, so it is the most significant bit. It is worth 8 and makes this number big.

0111 → The rightmost bit is 1, so it is the least significant bit. It is worth 1 and tells us the number is odd.

Flipping the leftmost bit of 0101 changes the number the most, because it has the biggest place value → 0101 -> 1101

The rightmost bit decides odd or even: 0 means the number is even → 1010 = 10 (even)

The most significant bit of 0110 is the 0 on the right. → The most significant bit is the leftmost bit, not the rightmost. In 0110 it is the 0 on the left.

1100 is odd because it starts with 1. → Odd or even depends on the rightmost bit, not the leftmost. 1100 ends in 0, so it is even (12).

Section C: Definitions

most significant bit — The leftmost bit of a binary number. It has the biggest place value, so it changes the number the most. The rightmost bit is the least significant bit.

Section D: Fill in the Blanks

Leftmost bit = most significant bit (MSB)

Rightmost bit = least significant bit (LSB)

In 8-bit binary, the left bit is worth 128

10111 ends in 1, so the number is odd

Place values from the right: 1, 2, 4, 8, 16

Section E: Spot the Error

D — A 1 in the least significant bit (the rightmost bit) means the number is odd. 1011 is 11, which is odd. The line should say 'odd'.

B — In a 5-bit number the leftmost bit (MSB) has the biggest place value, which is 16. A place value of 1 belongs to the rightmost bit (LSB).

B — A 0 in the rightmost bit (LSB) means the number is even. 0110 is 6, which is even. The line should say 'even'.

C — The least significant bit is the rightmost bit. In 1000 the rightmost bit is 0, not 1. The line should be LSB = 0.

C — 0101 is 5 and 1101 is 13, so the number changes by 8. The MSB has the biggest place value, so flipping it changes the number the most. It does not change it by just 1.