Question 684994: My number is prime and less than 25 the difference between the square of my number and the square of another prime number is 120 my number is the smaller of thw two primes. What's my number ?
Answer by Jolliano(16)   (Show Source):
You can put this solution on YOUR website! The question isn't complete but you can use reasoning to solve it.
List all the prime numbers which are less than 25
(2,3,5,7,11,13,17,19,23).
Since the difference the two squares is 120.
We take it that the squares of the two numbers must have the same last digit.
So taking two numbers that satisfies the rule above
*3 and 7:-
7^2 - 3^2 =49 - 9 =40 (X) WRONG!
*7 and 13:-
13^2-7^2=169-49=120
*If you carry out the operation on any other 2 numbers you wont get 120.
So the two numbers are 13 and 7.
Since your number is the smaller one,your number is 7.
|
|
|
