If \( x + \frac{1}{x} = 5 \), find \( x^2 + \frac{1}{x^2} \)
A number is increased by 20% and then decreased by 20%. What is the final result?
Find the sum:
\( 1+2+3+...+50 \)
Find the missing number:
2,6,7,21,22,66,?
If:
Find:
Find the smallest positive integer n that leaves a remainder of 3 when divided by 5, a remainder of 5 when divided by 7, and a remainder of 7 when divided by 9.
How many 3-digit numbers are there such that the sum of their digits is equal to 5?
A car was supposed to travel between two cities at a speed of 60 km/h. After driving half the distance, the car had to stop for 30 minutes. To arrive at the destination on time, the driver increased the speed to 80 km/h for the rest of the trip. What is the total distance between the two cities?
You have 400 grams of salt water that is 15% salt. How many grams of pure water must you add to make the mixture only 10% salt?
Find the value of this expression:
1/(1×2) + 1/(2×3) + 1/(3×4) + ... + 1/(19×20)
Currently, a father is 36 years old and his son is 8 years old. In how many years will the father be exactly 3 times as old as his son?
Alice and Bob have some marbles. At first, the ratio of Alice's marbles to Bob's marbles is 3 : 2. After Alice gives 10 marbles to Bob, they both have the same number of marbles. How many marbles did they have in total?