Question

Ritu was building a tower of LEGO blocks. She placed 4 blocks on the tower every minute, and took 60 minutes to finish the tower. When her brother joined her, together they were able to place 8 blocks on the tower for every minute. How long will it take to complete the tower now?

• A. 30 minutes
• B. 15 minutes
• C. 45 minutes
• D. 20 minutes

Answer 1

The correct option is A 30 minutes

If more people help out in the tower construction, it will take lesser time.
$\therefore$ This is a case of inverse proportion.
Using the formula for inverse proportion,
$\text{Number of blocks}\times \text{Time required}=constant$
$\Rightarrow 4\times 60=8\times \text{Time required}$
$\therefore$ Time required = $\frac{4\times 60}{8}$
= 30 minutes