JAMB Mathematics Past Questions & Answers - Page 148

736.

The smallest number such that when it is divided by 8 has a remainder of 6 and when it is divided by 9, has a remainder of 7 is

A.

387

B.

493

C.

502

D.

441

E.

634

Correct answer is C

Possible multiples of 8 and 9 = 72, 144, 216, 288, 360, 432, 576, 648.

\(\frac{387}{8}\) has remainder = 3; \(\frac{387}{9}\) has remainder 0.

\(\frac{493}{8}\) has remainder 5; \(\frac{493}{9}\) has remainder 7.

\(\frac{502}{8}\) has remainder 6; \(\frac{502}{9}\) has remainder 7.

\(\frac{441}{8}\) has remainder 1; \(\frac{441}{9}\) has remainder 0.

\(\frac{634}{8}\) has remainder 2; \(\frac{634}{9}\) has remainder 4.

Hence 502 is the answer.

738.

The vectors a and b are given in terms of two perpendicular units vectors i and j on a plane by a = 2i - 3j, b = -i + 2j. Find the magnitude of the vector a + 3b

A.

2

B.

4

C.

\(\sqrt{10}\)

D.

35

E.

2.2

Correct answer is C

a = 2i - 3j - 3i + 6j

= -i + 3j

= \(\sqrt{5 \times 2}\)

= \(\sqrt{10}\)

740.

Evaluate without using tables sin(-1290º)

A.

\(\frac{3}{2}\)

B.

-\(\frac{3}{2}\)

C.

\(\frac{2}{2}\)

D.

1

E.

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

Correct answer is E

sin(-1290º) = -sin(1290º)

sin([3*360] + 210)

where sin 360 = 0 and sin 210 = 180 + 30 ⇔ -30º

-sin ([3* 0] + [-30]) 

-sin(-30)

sin30 = \(\frac{1}{2}\)