How many permutations of a 7-digit phone number exist

"princess tower" in dubai is considered the world's tallest residential building, towering to 1 0 1 101 floors! t ( n ) t(n) models the number of tenants living on floor n n of the tower. what does the statement t ( 2 0 ) = t ( c ) t(20)=t(c) mean?

In priyas math class there are 10 boys and 15 girls. what is the ratio of boys to girls in priyas math class? express your answer as a decimal

Find two numbers if their ratio is 4: 7 and their difference is 123.