Page 51 - Maths Class 06
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At a Glance
l A factor of a number is an exact divisor of that number and the number has finite number of factors.
l A multiple of a number is exactly divisible by that number and the number can have infinite number
of multiples.
l Every number is a factor and multiple of itself.
l 1 is a factor of every number.
l 2 is the smallest and only even prime number.
l Two consecutive odd prime numbers are known as twin primes.
l Two numbers are said to be co-prime if they don’t have a common factor other than 1.
l Number 1 is neither prime nor composite .
l To know whether a given number is divisible by another number, we can use the divisibility test. It
makes the calculation simple and easier.
l If a number ‘a’ is exactly divisible by another number ‘b’, then ‘a’ is called a multiple of ‘b’; and ‘b’ is called
a factor of ‘a’.
l Number with only two factors, 1 and the number itself, are known as prime numbers.
l Numbers with more than two factors are called composite numbers.
l A number is divisible by 2, if its ones digit is 0, 2, 4, 6 or 8.
l A number is divisible by 3, if the sum of its digits is divisible by 3.
l A number is divisible by 4, if the last two digits of the number are divisible by 4.
l A number is divisible by 5, if the ones digit of the number is either 5 or 0.
l A number is divisible by 6, if the number is divisible by both 2 and 3.
l When two or more numbers are multiplied then each number is the factor of the product and
product is a multiple of each number.
l If a number is divided by its factor, the remainder is always zero.
Multiple Choice Questions
Tick (3) the correct answer:
1. The prime number is a number which:
(a) has exactly two factors (b) has three factors
(c) is divisible by 2 (d) has no factors
2. The HCF of 25 and 135 is:
(a) 3 (b) 5 (c) 9 (d) none
3. The largest 3-digit number of divisible by 3 is:
(a) 992 (b) 996 (c) 999 (d) 0
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