Andrew is about to leave for school. If he walks at a speed of 50 meters per minute, he will arrive 3 minutes after the bell rings. If he runs at a speed of 80 meters per minute, he will arrive 3 minutes before the bell rings. In how many minutes will the bell ring?

The answer is: 13 minutes

Step-by-step explanation:

First Let us form equations with the statements in the two scenario

Let the time in which the bell rings be 'x'

1. If Andrew walks (50 meters/minute), he arrives 3 minutes after the bell rings. Therefore the time of arrival at this speed = (3 + x) minutes

2. If Andrew runs (80 meters/minute), he arrives 3 minutes before the bell rings. Therefore the time taken to travel the distance = (x - 3) minutes

In both cases, the same distance is travelled, therefore, equation (1) = equation (2)

Next, collecting like terms:

dividing both sides by 3:

x =  390÷30 = 13

∴ x = 13 minutes

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is: