Find the number of permutations of the first 10 letters of the alphabet taking 2 letters at a time.

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.

What’s the answer? and how do i solve it ?

Sal is making bracelets for a fundraiser. he uses 6 inches of yarn per bracelet . how many bracelets can sal make with 5 feet of yarn