Question

the temperature of water is 80 degree Celsius after every 10 with the change in temperature minus 4 degree Celsius after how much time will be the temperature of water at 20 degree Celsius ​

Answer 1

Given :-

Current temperature of the water = 80°C

After every 10 seconds, the change in temperature is minus 4°C.

Let us suppose that the temperature changes after every 1 second for now instead of 10 seconds.

The first term = a = 80°C

Common difference = d = -4°C

AP :-

= 80, 80 + (-4), 80 + 2(-4), 80 + 3(-4) … 20

= 80, 76, 72, 68 … 20

Last term = An = 20°C

We know that,

a + (n - 1)d = An

➡ 80 + (n - 1)(-4) = 20

➡ 80 + (-4n + 4) = 20

➡ 80 - 4n + 4 = 20

➡ 84 - 4n = 20

➡ -4n = 20 - 84

➡ -4n = -64

➡ n = -64/-4

➡ n = 16

Hence, the temperature of the water will be after = 16 × 10 = 160 seconds