What does this rebus mean?

O
N
C
E
TIME

A mathematics teacher took exams for his students. Out of the total students, 25% passed both the tests included in the exam. However, only 42% were able to clear the first test.

Can you find out the percentage of those students who passed the first test and also passed the second test?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

Prove that twice of ten is the same as twice of eleven.

Solve the equation in the image by looking at the pattern closely.

Three fair coins are tossed in the air and they land with heads up. Can you calculate the chances that when they are tossed again, two coins will again land with heads up?

Can you find out who is the kidnapper in below Picture and why, Explain ?

Shyla was sleeping in her apartment when suddenly a robber broke into her house. He asked her to stay quiet and started looting the cash and jewelry. Suddenly the landline phone started ringing. The robber pointed a gun at Shyla and asked her to pick up and talk without giving away the situation.

She picked up the phone and it happened to be her husband. She spoke, Is it an emergency darling? Do give me a call when your flight lands, I will prepare your favorite food that will help you relieve the stress. Then she hanged up.

10 minutes after, the police arrive at the scene and catch the robber. How did the police know about the robbery?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

Before Mount Everest was discovered, what was the highest mountain in the world?