Three students have started a fence-painting business. Working together, Pragnesh and Qazi can paint the fence in 2 hours. Similarly, Pragnesh and Ronghui can paint the fence in 3 hours when they work together. Finally, when Qazi and Ronghui work together, they can paint the fence in 4 hours. How long would it take if all three students worked together to paint the fence.

in about 0.92 hours or 55.2 minutes

Step-by-step explanation:

The time they take to paint the room:

Pragnesh and Qazi  = 2 hours

Pragnesh and Ronghui = 3 hours

Qazi and Ronghui = 4 hours

Meaning, each hour (1)  they'll paint:

Pragnesh and Qazi  =   of the room

Pragnesh and Ronghui = of the room

Qazi and Ronghui = of the room

By summing all their work abilities we can determine how long it would take if all three students worked together to paint the fence, which is:

of the room each hour. Therefore the whole (1) room would be painted in 1 ÷ = or 0.92 hours or 55.2 minutes (0.92 * 60).