KJSEA 2025 Maths Q3 — Integers (Temperature Increase)
Published
The Question
“The temperature of a deep freezer was -8 degrees C. It was increased by 15 degrees. What is the new temperature?”
Turn the words into an operation
The freezer starts at a temperature below zero, and the word 'increased' tells us the temperature goes up. Going up means adding. So we add the 15 degree rise to the starting temperature of negative 8 degrees.
Picture it on a number line
Place the starting value at negative 8 on a number line. Adding a positive number means moving to the right, and we move one step for each degree. So from negative 8 we take 15 steps to the right.
Moving right increases a value; moving left decreases it.
Count past zero to the answer
The first 8 of those 15 steps bring us up to zero. That uses up 8 steps and leaves 15 minus 8, which is 7 steps still to take. Those 7 remaining steps carry us above zero to positive 7.
Final Result
The new temperature is +7 degrees C, which is option C.
Why this method works
Adding a positive integer to a negative one is really a subtraction of sizes: the 15 degree rise first cancels the 8 degrees below zero, and whatever is left over decides the result. Because 15 is larger than 8, the rise more than cancels the cold, so the answer is positive. The number line makes this visible because adding always moves you to the right, and crossing zero is just the moment the temperature stops being negative and becomes positive.
Reverse it: starting from +7 and cooling by 15 degrees gives 7 - 15 = -8 degrees C, the original temperature, so the answer is correct.