# Four Quarters Make A Dollar - How to Build Number Sense

Updated: Oct 28, 2022

Does math make sense? And how can you make sense of it?

In our recent newsletters, we shared some ideas on *building*** number sense. **As a challenge, we asked our members to compute

*"*__36 x 25__"*without*using long multiplication. It's quite tricky, and we were very happy to receive excellent solutions from both students and tutors!

Here, we present two solutions:

**Solution 1**: Recognize that 36 and 25 are both *perfect squares*.

36 x 25

= (6x6) x (5x5)

= (6x5) x (6x5)

= 30 x 30

= 900.

**Solution 2**: Use the fact that 4x25=100. Why is that? Because *4 quarters make a dollar!!*

36 x 25

= (9x4) x 25

= 9 x (4x25)

= 9 x 100

= 900.

These solutions show that we can use the ** multiplication chart** in different ways -- it's not just for multiplying two numbers together (9x4=36), but also for factoring a number (36=9x4). Indeed, when we look at a problem differently, we may find easy solutions.

It's important to memorize your multiplication chart by heart, so you can use it at ease. Having trouble memorizing it? Check out our __earlier blog __on the subject and learn some tricks!

Now, can you compute** "48 x 25"** without long multiplication? How about

**?**

*"*__64 x 125__"Challenge yourself! Have fun!