Question

If it takes eight men ten hours to build a wall, how long would it take four men?​

Answer 1

Given,

It takes eight men 10 hours to build a wall.

To Find,

The time taken by 4 men to do the same.

Solution:

As 8 men take 10 hours, 4 men would take more time as the no. of men is less.

Proportionating the values →

8: 10 :: 4: ?

Taking '?' as x and multiplying these proportions,

8 x 10 = 4x

80 = 4x

So, x = 80/4 = 20.

Therefore 4 men take 20 hours to complete the building of the wall.

Trick

→ We know that 8 is the double of 4. So when the no. of men is decreased, the time taken would be doubled. Therefore we can directly reach the answer as 10 x 2 = 20.

This trick can be used in competitive exams where multiple choice questions are provided to reduce time consumption.