Test of divisibility:
A number is divisible by ‘2’ if it ends in zero
or in a digit which is a multiple of ‘2’i.e.
2,4, 6, 8.
A number is divisible by ‘3’, if the sum of the
digits is divisible by ‘3’.
A number is divisible by ‘4’ if the number formed
by the last two digits, i.e. tens and
units are divisible by 4.
A number is divisible by ‘5’ if it ends in zero
or 5
A number is divisible by ‘6’ if it divisible by
‘2’ as well as by ‘3’.
A number is divisible by ‘8’ if the number formed
by the last three digits, i.e, hundreds
tens and units is divisible by ‘8’.
A number is divisible by ‘9’ if the sum of its
digit is divisible by ‘9’
A number is divisible by ‘10’ if it ends in zero.
A number is divisible by ‘11’ if the difference
between the sums of the digits in the
even and odd places is zero or a multiple of ‘11’.
LCM:
LCM of
a given set of numbers is the least number which is exactly divisible by
every number of the given set.
HCF:
HCF of
a given set of numbers is the highest number which divides exactly every
number of the given set.
Additional Rules
The square of an odd number is always odd.
A number is said to be a prime number if it is
divisible only by itself and unity. Ex. 1,
2, 3, 5,7,11,13 etc.
The sum of two odd number is always even.
The difference of two odd numbers is always even.
The sum or difference of two even numbers is
always even.
The product of two odd numbers is always odd.
The product of
two even numbers is always even.
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