Question

Write one digit on each side of 73 to make a four digit multiple of 36. How many different solutions does this problem have?

Answer 1

Answer: an option is 2736

and we only have two possible solutions, the other is 6732

Step-by-step explanation:

we want to write a number:

a73b, where a and b are one digit numbers (0 to 9) in such way that the number is divisible by 36.

Now, we know that 36 is multiple of 6, so 6*6 = 36

The multiples of 36 are always even numbers, so we can discard all the odd options for b.

We also can discard the option a = 0, because we want a 4 digit number.

now, let's do it by brute force.

if a = 1, we have:

173b, now you can give b different values (only even values) and see if some of them is divisible by 36. You will find that none is.

if a = 2

273b

when b = 6, we have:

N = 2736, that is divisible by 36 as:

2736/36 = 79, so this is a multiple of 36.

now, you can keep changing the value of a and find all the different possible solutions.

if a = 3,

373b is not divisible by 36 for any value of b

if a = 4

473b  is not divisible by 36 for any value of b

if a = 5

573b  is not divisible by 36 for any value of b

if a= 6

673b  it is divisible by 36 when b = 2.

6732/36 = 187

if a = 7

773b  is not divisible by 36 for any value of b

if a = 8

873b  is not divisible by 36 for any value of b

if a = 9

973b  is not divisible by 36 for any value of b

So we only have two possible solutions