Find a and b so that the following odd numbers are divisible by both 3 and 5:
(i)7b25 (ii) 8ab4b

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Solution

$(i) 7 b 25$
It is divisible by 5.
For it to be divisible by 3, $5 + b$ must be divisible by 3.
Therefore, $b = 1, 4, 7$

$(i i) 8 a b 4 b$
For the number to be odd and divisible by 5, $b = 5$
Now, for it to be divisible by 3, $4 + a$ must be divisible by 3.
Therefore, $a = 2, 5, 8$

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Find a and b so that the following odd numbers are divisible by both 3 and 5:(i)7b25 (ii) 8ab4b

(i)7b25It is divisible by 5.For it to be divisible by 3, 5+b must be divisible by 3.Therefore, b=1,4,7(ii)8ab4bFor the number to be odd and divisible by 5, b=5Now, for it to be divisible by 3, 4+a must be divisible by 3.Therefore, a=2,5,8

Find a and b so that the following odd numbers are divisible by both 3 and 5:
(i)7b25 (ii) 8ab4b

$(i) 7 b 25$
It is divisible by 5.
For it to be divisible by 3, $5 + b$ must be divisible by 3.
Therefore, $b = 1, 4, 7$

$(i i) 8 a b 4 b$
For the number to be odd and divisible by 5, $b = 5$
Now, for it to be divisible by 3, $4 + a$ must be divisible by 3.
Therefore, $a = 2, 5, 8$