Question : If the 4-digit number 48ab is divisible by 2, 5, and 7, then what is the value of (10a – b)?
Option 1: 0
Option 2: 20
Option 3: 10
Option 4: 30
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Correct Answer: 30
Solution :
The LCM of 2, 5, and 7 is 70.
Taking the 4-digit number which is divisible by 70 and lies between 4800 and 4900.
So, only one number exists(i.e. 70 × 69 = 4830). By equating both the numbers,
⇒ 48ab = 69 × 70 = 4830
On comparing,
⇒ a = 3 and b = 0
$\therefore$ (10a – b) = 30
Hence, the correct answer is 30.
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