Question

20 students of Class VI could make 40 paper lanterns in one hour. If 10 students from Class VII also joined them, how much time (in minutes) would be required to make the same number of lanterns?

• A. 30
• B. 40
• C. 60
• D. 120

Answer 1

The correct option is B 40

If the number of students making the lanterns increases, then the time required will decrease.

$\therefore$ This is a case of inverse proportion.

Initially, 20 students took 60 minutes to make 40 lanterns. Now, there are 20 + 10 = 30 students.

Using the formula for inverse proportion,
$\text{Number of students}\times \text{Time required (in minutes)}=\text{constant}$
$\Rightarrow 20\times 60=30\times \text{Time required (in minutes)}$
$\therefore$ Time required (in minutes) $=\frac{20\times 60}{30}=40$