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WAEC Further Mathematics Past Questions & Answers - Page 75

371.

Two forces (2i - 5j)N and (-3i + 4j)N act on a body of mass 5kg. Find in ms2, the magnitude of the acceleration of the body.

A.

25

B.

52

C.

25

D.

522

Correct answer is A

F=F1+F2

(2i5j)+(3i+4j)=(ij)

F=ma(1,1)=5a

a=(15,15)

|a|=(15)2+(15)2=225

|a|=25ms2

372.

Yomi was asked to label four seats S, R, P, Q. What is the probability he labelled them in alphabetical order?

A.

124

B.

16

C.

213

D.

14

Correct answer is A

The number of arrangements for the 4 letters = 4P4=4!(44)!

4!=24

Alphabetical order is just 1 of the arrangements for the letters 

= 124

373.

Find the direction cosines of the vector 4i3j.

A.

910,2710

B.

1727,1727

C.

45,35

D.

47,37

Correct answer is C

Given V=xi+yj, the direction cosines are x|V|,y|V|.

|4i3j|=42+(3)2=25=5

Direction cosines = 45,35.

374.

If OA=3i+4j and OB=5i6j where O is the origin and M is the midpoint of AB, find OM

A.

-2i - 10j

B.

-2i + 2j

C.

4i - j

D.

4i + j

Correct answer is C

OA=(3,4)

OB=(5,6)

OM=(3+52,4+(6)2)

= (4,1)=4ij

375.

Find the least value of n for which 3nC2>0,nR

A.

13

B.

16

C.

23

D.

1

Correct answer is C

3nC2>03n!(3n2)!2!>0

3n(3n1)(3n2)!(3n2)!2>0

3n(3n1)2>0

3n(3n1)>0n>0;n>13

The least number in the option that satisfies n>0;n>13=23