Shortcut Trick
For 45yz0 to be divisible by 40, dividing it by 10 means 45yz must be divisible by 4.
A number is divisible by 4 if its last two digits form a multiple of 4.
So, the two-digit number 'yz' must be a multiple of 4.
The largest possible two-digit multiples of 4 are 96 (sum = 15) and 88 (sum = 16).
Thus, the maximum possible value for the sum of digits (y + z) is 16.
∴ The correct answer is 16.
Alternate Method
Given:
The 5-digit number is 45yz0.
The number is perfectly divisible by 40.
Concept Used:
A number is divisible by 40 if it is divisible by both 8 and 5.
Since the last digit is 0, it is already divisible by 10 (and hence 5).
For the number to be divisible by 40, removing the last 0 means the remaining number must be divisible by 4.
Calculation:
⇒ Number = 45yz0
⇒ Since 45yz0 is divisible by 40, then (45yz0 ÷ 10) must be divisible by 4.
⇒ This implies 45yz is divisible by 4.
⇒ According to the divisibility rule of 4, the number formed by the last two digits 'yz' must be a multiple of 4.
⇒ We need to find the maximum possible sum (y + z) where y and z are single digits from 0 to 9.
⇒ Let's check the largest possible two-digit multiples of 4:
⇒ If yz = 96, sum of digits (y + z) = 9 + 6 = 15
⇒ If yz = 92, sum of digits (y + z) = 9 + 2 = 11
⇒ If yz = 88, sum of digits (y + z) = 8 + 8 = 16
⇒ If yz = 84, sum of digits (y + z) = 8 + 4 = 12
⇒ If yz = 76, sum of digits (y + z) = 7 + 6 = 13
⇒ We can see that the maximum possible sum occurs when y = 8 and z = 8.
⇒ Maximum (y + z) = 8 + 8 = 16.
∴ The correct answer is 16.
Additional Information
Divisibility Rule of 4
A number is divisible by 4 if the last two digits of the number form a multiple of 4 (e.g., 12, 24, 88).
Divisibility Rule of 8
A number is divisible by 8 if the last three digits form a multiple of 8 (e.g., 104, 880).
Composite Divisors
To check divisibility by a composite number like 40, verify if the number is divisible by its co-prime factors, such as 5 and 8.