Which of the following statements are true?
(i) If a number is divisible by 3, it must be divisible by 9.
(ii) If a number is divisible by 9, it must by divisible by 3.
(iii) If a number is divisible by 4, it must by divisible by 8.
(iv) If a number is divisible by 8, it must be divisible by 4.
(v) A number is divisible by 18, if it is divisible by both 3 and 6.
(vi) If a number is divisible by both 9 and 10, it must be divisible by 90.
(vii) If a number exactly divides the sum of two numbers, it must exactly divide the numbers separately.
(viii) If a number divides three numbers exactly, it must divide their sum exactly.
(ix) If two number are co-prime, at least one of them must be a prime number.
(x) The sum of two consecutive odd numbers is always divisible by 4.
(i) If a number is divisible by 3, it must be divisible by 9.
False, as any number following criteria of 9n + 3 or 9n + 6 violates the statement.
For example, 6, 12,…
(ii) If a number is divisible by 9, it must by divisible by 3.
True, as 9 is multiple of 3.
Hence, every number which is divisible by 9 must be divisible by 3.
(iii) If a number is divisible by 4, it must by divisible by 8.
False, as any number following criteria of 8n + 4 violates the statement.
For example, 4, 12,20,….
(iv) If a number is divisible by 8, it must be divisible by 4.
True, as 8 is multiple of 4.
Hence, every number which is divisible by 8 must be divisible by 4.
(v) A number is divisible by 18, if it is divisible by both 3 and 6.
False, for example 48, which is divisible to both 3 and 6 but not divisible with 18
(vi) If a number is divisible by both 9 and 10, it must be divisible by 90.
True, as 90 is the GCD of 9 and 10.
Hence, every number which is divisible by both 9 and 10, it must be divisible by 90.
False, for example 6 divides 30, but 6 divides none of 13 and 17 as both are prime numbers.
(viii) If a number divides three numbers exactly, it must divide their sum exactly.
True, if x,y and z are three numbers, where each of x, y and z is divided by a number (say s), then (x+y+z) is divided by s
(ix) If two number are co-prime, at least one of them must be a prime number.
False, as 16 and 21 are co prime but none of them is prime.
(x) The sum of two consecutive odd numbers is always divisible by 4.
True.