Page 6 - Arithmetic

Worked Example 3
Is 6760 divisible by 8?
Solution:
A number is divisible by 8 if the last three digits are divisible by 8. Last two digits = 760
760 is divisible by 8.
So, 6760 is divisible by 8.
Worked Example 4
Which of the following is a prime number? a) 93
b) 115
c) 411
d) 121 e) 139
Solution:
a) Clearly, 93 is divisible by 3. The sum of numbers (9 + 3 = 12) is divisible by 3. So, this is not a prime number.
b) The number ends in 5, which means it’s divisible by 5. So, this is not a prime number.
c) The sum of the numbers (4 + 1 + 1= 6) is divisible by 3. So, this is not a prime number.
d) The sum of number at odd places = 1 + 1 = 3. The sum of the numbers at even places = 2.
Difference = 3 – 2 =1. So, the number is divisible by 11. So, this is not a prime number.
e) 12>√139. Prime numbers less than 12 are 2, 3, 4, 7, and 11. 139 is not divisible by all the numbers. So, it’s a prime number.
Answer: 139
Remainder
It’s the amount which is left after division. You come across a remainder when a particular number is not completely divisible by the other.
For example
21 is not divisible by 4. The nearest you can reach 21 is 20, which is one less than 21. So, the remainder is 1.
REMEMBER:
Dividend = (Quotient × Divisor) + Remainder
In the above example, 21 is the dividend, 4 is the divisor, 1 is the remainder and the quotient is 5..
Page 5 of 55
Arithmetic Concept