Math Class Nine

Answer Key
Attempt all questions.
 Solve:
 
 Answer:   

⦁ Solve      18.9 × 0.456
Answer:        8.6184 
⦁ Find LCM of 21, 27, 51, and 81 by division method.
Solution:
3 21, 27, 51, 81
3 7,  9, 17, 27
3 7,  3, 17, 9
3 7, 1, 17, 3
7 7 , 1, 17, 1
17 1, 1, 17, 1
1, 1, 1, 1




Thus, LCM = 3 × 3 × 3 ×3 × 7 × 17 = 9639
⦁ Find the perimeter and area of a rectangle with length 6cm and breadth 3cm.
Solution:  Given that length (l) = 6 cm and breadth (b) = 3cm
                            Perimeter =  2 × (l + b)
= 2 × (6cm  + 3 cm)  = 2 × 9cm = 18 cm
Area =  l × b  =  18 cm2

⦁ Define supplementary and complementary angles
Prime Numbers: A prime number is a whole number greater than 1 which has exactly two factors. i. e 1 and the number itself.
For example, 2, 3, 5, 7, 11, 13, 19, 23, etc are all the prime numbers.
Composite numbers:  Numbers having more than 2 factors are composite numbers. The numbers 4, 6, 8, 9, 10, 12, 14, 15, 16, ………. have more than two factors so these are composite numbers.

⦁ Define supplementary and complementary angles.
  Supplementary Angles: If the sum of measures of two angles is 1800, then these angles are called supplementary angles.




These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°.
  Complementary Angles:  If the sum of measures of two angles is 900, then these angles are called complementary angles.




These two angles (40° and 50°) are Complementary Angles, because they add up to 90°.