What is the smallest positive 2-digit whole number divisible by 3 and ...
Let xy be the whole number with x and y the two digits that make up the number. The number is divisible by 3 may be written as follows
10 x + y = 3 k
The sum of x and y is equal to 9.
x + y = 9
Solve the above equation for y
y = 9 - x Substitute y = 9 - x in the equation 10 x + y = 3 k to obtain.
10 x + 9 - x = 3 k
Solve for x
x = (k - 3) / 3
x is a positive integer smaller than 10
Let k = 1, 2, 3, ... and select the first value that gives x as an integer. k = 6 gives x = 1
Find y using the equation y = 9 - x = 8
The number we are looking for is 18 and the answer is D. It is divisible by 3 and the sum of its digits is equal to 9 and it is the smallest and positive whole number with such properties.
View all questions of this test
What is the smallest positive 2-digit whole number divisible by 3 and ...
Problem:
What is the smallest positive 2-digit whole number divisible by 3 and such that the sum of its digits is 9?
Solution:
To solve this problem, we need to find the smallest 2-digit number that is divisible by 3 and has a digit sum of 9.
Step 1: Finding the Divisibility Rule
To determine if a number is divisible by 3, we can check if the sum of its digits is divisible by 3. In this case, we need to find a number whose digits add up to 9.
Step 2: Identifying the Possible Numbers
Since we are looking for a 2-digit number, the possible numbers range from 10 to 99. Let's list all the possible numbers and their digit sums:
10: 1 + 0 = 1
11: 1 + 1 = 2
12: 1 + 2 = 3
...
98: 9 + 8 = 17
99: 9 + 9 = 18
Step 3: Finding the Smallest Number
Out of all the possible numbers, we can see that 12 and 18 have digit sums of 3 and 9, respectively. However, 12 is not divisible by 3, so we can eliminate it.
Therefore, the smallest 2-digit number that is divisible by 3 and has a digit sum of 9 is 18.
Answer:
Hence, the correct answer is option 'D' - 18.