Thirty men working at a rate of 10 hours a day can complete a job in 14 days. Find how long it would take 40 men working at the rate of 7 hours a day to complete the same job.

Jumla ya saa za kazi = Idadi ya wanaume $\times$ Saa kwa siku $\times$ Idadi ya siku

$$\text{Jumla ya saa za kazi} = 30 \text{ wanaume} \times 10 \text{ saa/siku} \times 14 \text{ siku}$$ $$\text{Jumla ya saa za kazi} = 300 \times 14$$ $$\text{Jumla ya saa za kazi} = 4200 \text{ saa za kazi}$$

Tunajua kwamba wanaume 40 wanafanya kazi saa 7 kwa siku.
Acha $D_2$ iwe idadi ya siku zinazohitajika.

$$40 \text{ wanaume} \times 7 \text{ saa/siku} \times D_2 \text{ siku} = 4200 \text{ saa za kazi}$$ $$280 \times D_2 = 4200$$

Gawanya pande zote mbili kwa 280.

$$D_2 = \frac{4200}{280}$$ $$D_2 = \frac{420}{28}$$ $$D_2 = 15 \text{ siku}$$

Itachukua wanaume 40 wanaofanya kazi saa 7 kwa siku siku 15 kukamilisha kazi hiyo hiyo.

The final answer is $\text{15 days}$.