Question

The diagram shows a flood warning post in a river. The water level rises by 1 meter. The new water level is cm.

Answer 1

Initial water level = - 20 cm
The water level rises by 1 meter.
We know, 1 meter = 100 cm

The final water level
$=(-20)+100=(-20)+(+100)$ cm

To subtract integers with opposite sign, we follow the below steps:

Step 1 : Take absolute value of both the numbers.

$|-20|=20$ and $|+100|=100$

Step 2 : Subtract the smaller absolute value from the larger absolute number.

$100-20=80$

Step 3 : Assign the sign associated with the original greater number to the result of subtraction.
$\Rightarrow +80$ cm

$\therefore$ The new flood level reading is $80$ cm.