Linear equations and inequalities

1003197407

Level: 
C
A hose can fill the garden pool in 20 hours. The owners bought a pump that guarantees filling the pool in 8 hours. However, a crack appeared in the pool's shell which can drain all the water from the full pool within 5 days. How long will it take to fill the pool with the hose and the pump at the same time as the water runs off through the crack?
exactly 6 hours
approximately 5.7 hours
approximately 5.5 hours
approximately 6.8 hours

1003197408

Level: 
C
The painter A takes 15 hours to paint a flat. The painter B takes 12 hours to paint the same flat and the painter C takes 10 hours to complete the same task. The painter A starts to paint alone and after 2 hours joins him the painter B. After the next hour the painter C starts to paint with them too. How long will all three painters paint together before completing the work?
2h 52min
3h 8min
3h 24min
4h

2010011202

Level: 
C
Students registered for sports camps. For the biking camp registered by 12 students more than for the boating camp. After some time one of the students switched his registration from the boating camp to the biking camp. Now, there is three times more bikers than boaters. How many students registered originally for the biking camp?
20
21
7
8

9000018110

Level: 
C
Consider a coil composed from a ferrite core and a wire winding. The mass of the core is 2kg. The material for the wire is such that the mass of the wire of the length 30m is bigger than the mass of the wire of the length 10m together with the ferrite core. In the following list identify a possible mass of one meter of the wire.
110g
100g
0.01kg
0.09kg