Mathematics · May / June 2025 · Paper 21 · Question 1

1

−

4x

7 6 ...

×

7 6 5 ...

××

Correct form for term 3 or term 4: Either

(

)

2

or

(

)

3

o.e.

x

x

2

6

7

×

6

7

××

6 5

(

)

2

or

(

)

3

o.e.

−

4

x

−

4

x

2

6

1 28

336

2

2240

3

= −

x

+

x

−

x

Sets "336" 5 "28"k

×−

= 1316

(

) 13

k =

(a) Note that a correct expression scores 4/4

M1: Correct form for

2x or

3x . Look for the correct binomial coefficient with the correct power of x. You do

not need to be concerned with the 4

− which may have been omitted.

Allow alternative equivalent notation for the binomial coefficient for this mark e.g. 7

C or 7

2

or 7!

2!5! etc

Condone invisible brackets for this mark e.g. 7

2 1

5

−

4

2

C

x

A1: Correct

2x or

3x term (which may be unsimplified). They must have a numerical expression or value

for their binomial coefficient for this mark. i.e. do not allow e.g. 7

C

3

Do not condone poor bracketing for this mark but may be implied by further work.

B1: For the series starting 1 28x

−

(terms may be in any order or as a list)

Condone

1

−

28x

1

but not e.g. 1

+−

28x

isw if they subsequently incorrectly attempt to simplify their answer.