JAMB Mathematics Past Questions & Answers - Page 31

151.

A trapezium has two parallel sides of lengths 5cm and 9cm. If the area is 91cm\(^2\), find the distance between the parallel sides

A.

13 cm

B.

4 cm

C.

6 cm

D.

7 cm

Correct answer is A

Area of Trapezium = 1/2(sum of parallel sides) * h
91 = \(\frac{1}{2}\) (5 + 9)h

cross multiply
91 = 7h
h = \(\frac{91}{7}\)
h = 13cm

152.

Determine the maximum value of y=3x\(^2\) + 5x - 3

A.

6

B.

0

C.

2

D.

No correct option

Correct answer is D

y=3x\(^2\) + 5x - 3

dy/dx = 6x + 5

as dy/dx = 0

6x + 5 = 0

x = \(\frac{-5}{6}\)

Maximum value: 3 \( ^2{\frac{-5}{6}}\)  + 5 \(\frac{-5}{6}\) - 3

3 \(\frac{75}{36}\) - \(\frac{25}{6}\) - 3

Using the L.C.M. 36

= \(\frac{25 - 50 - 36}{36}\)

= \(\frac{-61}{36}\)

No correct option

153.

Solve the following equation: \(\frac{2}{(2r - 1)}\) - \(\frac{5}{3}\) =  \(\frac{1}{(r + 2)}\)

A.

( -1,\(\frac{5}{2}\) )

B.

( 1, - \(\frac{5}{2}\) )

C.

( \(\frac{5}{2}\), 1 )

D.

(2,1)

Correct answer is B

\(\frac{2}{(2r - 1)}\) - \(\frac{5}{3}\) =  \(\frac{1}{(r + 2)}\)

\(\frac{2}{(2r - 1)}\) - \(\frac{1}{(r + 2)}\)  = \(\frac{5}{3}\)

The L.C.M.: (2r - 1) (r + 2) 

\(\frac{2(r + 2) - 1(2r - 1)}{(2r - 1) (r + 2)}\) = \(\frac{5}{3}\)

\(\frac{2r + 4 - 2r + 1}{ (2r - 1) (r + 2)}\) = \(\frac{5}{3}\)

cross multiply the solution

3 * 5 = (2r - 1) (r + 2) * 5

divide both sides 5

3 =  2r\(^2\) + 3r - 2 (when expanded)

collect like terms

2r\(^2\) + 3r - 2 - 3 = 0

2r\(^2\) + 3r - 5 = 0

Factors are -2r and +5r

2r\(^2\) -2r + 5r - 5 = 0

[2r\(^2\) -2r] [+ 5r - 5] = 0

2r(r-1) + 5(r-1) = 0

(2r+5) (r-1) = 0

 r = 1 or - \(\frac{5}{2}\)

154.

The fourth term of an Arithmetic Progression (A.P) is 37 and the first term is -20. Find the common difference.

A.

3

B.

57

C.

19

D.

17

Correct answer is C

a + 3d = 37

-20 + 3d = 37 

3d = 37 + 20 = 57

d = \(\frac{57}{3}\) 

= 19

155.

If 7 + y = 4 (mod 8), find the least value of y, 10 \(\leq y \leq 30\) 

A.

11

B.

13

C.

19

D.

21

Correct answer is B

7 + y = 4 (mod 8)

y = 4 - 7 (mod 8)

y = -3 + 8 (mod 8) 

y = 5 + 8 (mod 8)

y = 13