Quadratic Formula - Part 3 - Solving without a calculator

How to solve a quadratic equation using the formula, sometimes leaving your answer in 'surd' form

[jamesderek]

Thanks sir, this is the video I really want, it's the one that taught me how to "mentally solve" or solve "without a calculator". So much appreciated sir!!!

[MrBoultonMaths]

Hi Nabeel.

First, every number must be rounded to 1 significant figure, so it becomes:

7 x 200 / 0.05

Next line:

1400/0.05

Multiply top and bottom by 100, so you get a whole number in the denominator, then evaluate:

140, 000 / 5 = 28, 000

***

I suspect when you rounded, you did: 7 x 100 / 1, which would give you 700. Am I right?

[BobBob-qytl]

You have to also get the positive number

[anonymousbullet]

sir its Nabeel, and i forgot how to find out an estimate for a value. The question is 6.8 x 191 divided by 0.051 and i just tried to remember but i dont know if i got it right or not! my answer was 700 :S

[MrBoultonMaths]

...not sure how you got 2500. Does the explanation above make sense at least?