Question

Each crop duster who works in a firm can dust half an acre of crops in $25$ minutes. The company must dust eight $0.75$-acre lots and twelve $1.5$-acre lots to complete a certain job. Calculate the minimum number of crop dusters needed to complete the job in $5$ hours.

• A. $4$
• B. $5$
• C. $6$
• D. $7$

Answer 1

The correct option is A $4$

There are two different size lots:

$0.75$ acre and $1.5$ acre

If a crop duster can dust $0.5$ acre in $25$ minutes, then they can dust $0.75$ acre in $\frac{0.75\times 25}{0.5}=37.5$ minutes.

That same crop duster can dust a $1.5$ acre lot in $\frac{1.5\times 25}{0.5}=75$ minutes

Now,

We have $45$ hours or $300$ minutes.

In $5$ hours a crop duster can dust

$4,1.5$-acre lots or $8,0.75$-acre lots

There are $12,1.5$-acre lots, so $3$ dusters will be needed.

There are $8,0.75$-acre lots, so $1$ crop duster will be needed here.

$\therefore 3+1=4$

Hence, they will need $4$ crop dusters to complete the job in $5$ hours.