$3x ≡ 4(mod 5)$. Find the least value of x

The interquartile range of a distribution is 7. If the 25th percentile is 16, find the upper quartile.

Two buses start at the same station from 9.00 a.m. and travel in opposite directions along the same straight road. The first bus travels at a speed of 72 km/h and the second at 48 km/h. At what time will they be 240 km apart?

A student measures a piece of rope and found that it was 1.26m long. If the actual length of the rope was 1.25m, what was the percentage error in the measurement.