On a cold February morning, the radiator fluid in Stanley's car is - 18 degrees When the engine is running, the temperature goes up 4.5 degrees per minute. Approximately how long will it take before the radiator fluid temperature reaches 60 degrees?

Remark

This is an arithmetic progression. You have the first and last terms and the difference.

Givens

a = - 18

L = 60

d = 4.5

Equation

L = a + (n - 1) d

Solve

60 = - 18 + (n - 1) * 4.5 Add 18 to both side

60 + 18 = (n - 1) * 4.5

78 = (n - 1) * 4.5 Divide both sides by 4.5

78/4.5 = n - 1

17.3333 = n - 1 Add 1 to both sides.

18.3333 = n

Conclusion

It will that 18 1/3 or 18.33333 minutes to get the from - 18 to 60 degrees.