Shortcut Trick
LCM of 12, 16, and 24 is 48.
The required number format is 48k + 4.
Divide the upper limit 5000 by 48 ⇒ Remainder = 8.
Highest multiple of 48 under 5000 = 5000 − 8 = 4992.
Required highest number = 4992 + 4 = 4996.
∴ The correct answer is 4996.
Alternate Method
Given:
Divisors = 12, 16, and 24
Range = 4000 to 5000
Remainder = 4
Concept Used:
Number = LCM of divisors × k + Remainder
Calculation:
⇒ Prime factors of 12 = 22 × 3
⇒ Prime factors of 16 = 24
⇒ Prime factors of 24 = 23 × 3
⇒ LCM(12, 16, 24) = 24 × 3 = 16 × 3 = 48
⇒ The required number must be of the form N = 48k + 4.
⇒ Divide 5000 by 48 to find the highest multiple under 5000.
⇒ 5000 ÷ 48 = 104 with a remainder of 8.
⇒ Highest multiple of 48 under 5000 = 5000 − 8 = 4992.
⇒ Substitute the multiple back to find the number:
⇒ N = 4992 + 4 = 4996.
⇒ 4996 clearly lies within the target range of 4000 to 5000.
∴ The correct answer is 4996.
Additional Information
LCM with Constant Remainder
When finding a number that leaves the same remainder r when divided by a, b, and c, use the form: N = LCM(a, b, c) × k + r.
LCM with Different Remainders
If a number divided by a, b, and c leaves remainders x, y, and z respectively, and the difference is constant (a−x = b−y = c−z = K), the number format is: N = LCM(a, b, c) × k − K.
HCF with Given Remainders
The greatest number that divides a, b, and c leaving remainders x, y, and z respectively is given by HCF of (a−x), (b−y), and (c−z).