When Arpita was going through her address book, she glanced upon the telephone number of her old friend, Gita. However, the last two digits were erased. But being a math freak, Arpita remembered that Gita had a 6 digit telephone number starting with 2345_ _ whose digital sum =7 (digital sum is the sum of the digits of a number till a single digit number is obtained). Find the maximum number of trials till she dials the right number.
When Arpita was going through her address book, she glanced upon the telephone number of her old friend, Gita. However, the last two digits were erased. But being a math freak, Arpita remembered that Gita had a 6 digit telephone number starting with 2345_ _ whose digital sum =7 (digital sum is the sum of the digits of a number till a single digit number is obtained). Find the maximum number of trials till she dials the right number.
The correct option is D 11
As of now the sum is 14. Let the last two digits be a and b.
With an upper limit of 9 for a and b:
a+b = 2 and a+b = 11
Number of solutions for a+b = 2 is 3 [(0,2), (2, 0), (1, 1)].
Number of solutions for a+b = 11 is 8 (12C1−4=8)
Total number of ways = 11
Shortcut:
The question is about an AP with common difference = 9 in a span of 100 numbers. Answer is 1009=11.
11
As of now the sum is 14. Let the last two digits be a and b.
With an upper limit of 9 for a and b:
a+b = 2 and a+b = 11
Number of solutions for a+b = 2 is 3 [(0,2), (2, 0), (1, 1)].
Number of solutions for a+b = 11 is 8 (12C1−4=8)
Total number of ways = 11
Shortcut:
The question is about an AP with common difference = 9 in a span of 100 numbers. Answer is 1009=11.
