4 is increased to 23​

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

In a two-digit number the units' digit is 7 more than the tens' digit. the number with digits reversed is three times as large as the sum of the original number and the two digits. find the number.

The sum of the squares of two numbers is 8 . the product of the two numbers is 4. find the numbers.