# 2019 JAMB-UTME mathematics question 36

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If S = (4t + 3)(t – 2), find ds/dt when t = 5secs.

• A. 50 units per sec
• B. 35 units per sec
• C. 13 units per sec
• D. 22 units per sec

B

## SOLUTION…

We can resolve this problem with two different methods, whichever way results in the same answer.

Method 1 = carrying out the multiplication and expanding to remove the bracket, and then differentiating the result using normal differentiation formula before substituting t = 5secs to get our answer.

Method 2 = using product rule to differentiate and then substituting t = 5secs.

Here, we are going to use method 2,

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Product rule states thus:

### Now for the right answer to the above question:

1. Option A is incorrect.
2. Option B is correct.
3. C is incorrect.
4. D is not the correct answer.