Page 19 - SM inner class 6.cdr

Composite Numbers

A number having factors other than 1 and itself is called a composite number or we can say that
the numbers having more than two factors are composite numbers, i.e. 4, 6, 8, 9, 10 … are all
composite numbers because each of these numbers has more than two factors.

E xercise 3.1

1. Write all factors of each of the follow ing numbers.
(i) 21 (ii) 36 (iii) 48 (iv) 99
2. Write first five multi plies of each of the follow ing numbers.
(i) 3 (ii) 5 (iii) 9 (iv) 12
3. Sepa rate the odd and even numbers.
(i) 135 (ii) 342 (iii) 1112 (iv) 5008
(v) 9427 (vi) 8134 (vii) 10006 (viii) 78965
4. List all prime numbers between:
(i) 10 and 50 (ii) 25 and 60 (iii) 32 and 48 (iv) 76 and 90

5. List all numbers less than 100 which are multi ples of 5 and 10.
6. List all numbers less than 50 which are multi ples of 3 and 4.
7. Write all compos ite numbers less than 20.
8. Write five consec u tive compos ite numbers just below 50.
9. Write all prime numbers less than 15

Divisibility Test

Divisible By Test Example

3,489,076:
Last digit even or 0 = (0, 2, 4, 6 or 8)
2 Last digit = 6
or Multiples of 2
6 = 3 2
´
16,499,205,854,376:
Add up all the digits in the number.
+
+
+
+
+
+
+
+
+
+
+
1 6 4 9 9 2 0 5 8 5 4 3
3 Repeat until sum is 2-digits. If
+ + 6 = 69
7
2-digits divisible by 3
6 9 = 15 Þ 15 = 5 3
´
+
1. Las two digits divisible by 4 358,912:
4 2. Tens digit even and ones digit = 0, 4, or 8 1. Last 2 digits = 12 Þ12 = 3 4
´
Tens digit odd and ones digit = 2 or 6 2. Tens digit = 1, odd and ones digit = 2
3,783,953,495:
5 Last digit = 5 or 0
Last digit = 5
57,342:
Last digit = 2 which is divisible by 2 and
6 Divisible by 2 (even) and 3
+
+
5 7 3 4 2 = 21
+
+
21 = 7 3
´
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Mathematics In Focus - 6