When wiring a house, an electrician knows that the time she will take is given by the formula Time= 2 hours + 12 minutes per lightswitch. She charges her customers a call out fee of £35, plus £20 per hour. How much should a customer be charged for wiring a house with 10 lightswitches?​

Step-by-step explanation:

Time = 2 hrs + 12 min (10) = 4 hrs.

Cost = 35 + 20*4

Cost = 35+80

Cost = 115

9514 1404 393

  £155

Step-by-step explanation:

We can write the function describing the charges as a composition.

  t(s) = 2 + 12/60s = 2 +s/5 . . . . . hours for s switches

  c(h) = 35 +30h . . . . . . . . . . . . . charge for h hours

Then the charge for s switches is ...

  f(s) = c(t(s)) = 35 +30(2 +s/5) = 35 +60 +6s

  f(s) = 95 +6s . . . . . . . charge for installing s switches

The charge for 10 switches is then ...

  f(10) = 95 +6·10 = 95 +60

  f(10) = 155 . . . . pounds

The electrician should charge her customer £155 for wiring a house with 10 switches.

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