# Exam-Style Questions.

## Problems adapted from questions set for previous Mathematics exams.

### 1.

IB Studies

While studying a new disease, scientists found that the number of toxic cells in the bloodstream increased over time, according to the model $$D(t)=12×(1.16)^t , t \ge 0$$ where $$D$$ is the number of the toxic cells in the bloodstream per litre and $$t$$ is the time in hours.

(a) Find the number of toxic cells in the bloodstream at $$t=0$$.

(b) Calculate the number of toxic cells in the bloodstream after 3 hours.

(c) Determine the time it takes for the number of toxic cells in the bloodstream to first exceed to 200 per litre. Give your answer to the nearest minute.

### 2.

IB Studies

The diagram show a wheelchair ramp from ground level to a height of 70cm.

(a) Calculate the gradient of the ramp.

Ramp manufacturers recommend a gradient no steeper than 1:12 for safe independent use.

(b) Using your answer to part (a), comment on whether this wheelchair ramp is safe for independent use.

The equation of a different wheelchair ramp is $$2x + 22y -1860 = 0$$ where $$y$$ represents the height and $$x$$ the horizontal distance, both in centimetres.

(c) Find the horizontal distance covered by this wheelchair ramp.

(d) Determine whether this wheelchair ramp is safe for independent use.

### 3.

IB Standard

Percy Cod and Fran Finklestein are both researchers working at different universities. They are each studying a different colony of bacteria which coincidentally start increasing in size at the same time.

The number of bacteria in Percy's colony, after $$t$$ hours, is modelled by the function $$P(t)=8e^{0.3t}$$.

(a) Find the initial number of bacteria in Percy's colony.

(b) Find the number of bacteria in Percy's colony after four hours.

(c) How long does it take for the number of bacteria in Percy's colony to reach 350?

The number of bacteria in Fran's colony, after t hours, is modelled by the function $$F(t)=16e^{kt}$$.

(d) After four hours, there are 35 bacteria in Fran's colony. Find the value of $$k$$.

(e) The number of bacteria in Percy's colony first exceeds the number of bacteria in Fran's colony after $$n$$ hours, where $$n\in \mathbf Z$$. Find the value of $$n$$.

### 4.

GCSE Higher

The quantity of heat required to heat an amount of water is given by the formula:

$$H = atI^2 – b$$

Where $$H$$ is the number of calories delivered by an electric current of $$I$$ amps acting for $$t$$ seconds and $$a$$ and $$b$$ are constants.

(a) Rearrange the formula to make $$I$$ the subject.

The graph below gives information about the cooling of a cup of coffee on a cold day. The vertical axes shows the variation in the temperature, $$T$$, and the horizontal axis shows the time, $$t$$, in seconds.

(b) Work out the average rate of decrease of the temperature of the coffee between $$t = 0$$ and $$t = 700$$.

The instantaneous rate of decrease of the temperature of the water at time $$A$$ seconds is equal to the average rate of decrease of the temperature of the water between $$t = 0$$ and $$t = 700$$.

(c) Find an estimate for the value of $$A$$ showing how you got your answer.

### 5.

IB Applications and Interpretation

In a fantasy story the power value of a dream catcher varies depending on its length. The power values of various dream catchers are recorded in the following table:

 Length, $$x$$ cm 0 10 15 Power, $$p$$ W 0 12 22

This information was used to create Model A, where $$p$$ is a function of $$x$$ , $$x \ge 0$$.

Model A: $$p(x) = ax^2 + bx$$ , where $$a,b \in \mathbb{Z}$$.

When the length is 10 cm, Model A can be represented by the equation 50a + 5b = 6.

(a) Write down a second equation to represent Model A, when the length is 15cm.

(b) Find the values of a and b.

(c) Find the coordinates of the vertex of the graph of $$y = p(x)$$.

(d) Using the values in the table and your answer to part (c), sketch the graph of $$y = p(x)$$ for $$0 \le x \le 15$$ and $$0 \le p \le 22$$.

Additional data was used to create Model B, a revised model for the power of a dream catcher.

Model B: $$p(x) = 0.06x^2 + 0.68x$$

(e) Use Model B to calculate an estimate for the power of a dream catcher of length 18cm.

The actual power of a dream catcher of length 18cm is 30 W.

(f) Calculate the percentage error in the estimate in part (e).

### 6.

IB Standard

A Big Wheel at an amusement park has a diameter of length 70 metres which rotates at a constant speed. The bottom of the wheel is h metres above the ground. A seat starts at the bottom of the wheel.The wheel completes one revolution in 4 minutes. [The diagram is not to scale]

(a) After 2 minutes, the seat is 76m above the ground. Find h.

(b) After t minutes, the height of the seat above ground is given by $$f(t) =41+ k \cos{ \frac{\pi t}{2}}$$ for $$0 \le t \le 16$$.
Find the value of k.

(c) Find when the seat is 40 m above the ground for the third time.

### 7.

IB Studies

A cup of hot tea is placed on a table to cool. The temperature of the room is 24oC.

This situation can be modelled by the exponential function:

$$T = a + b (k^{-m})$$

where $$T$$ is the temperature of the water, in oC, and $$m$$ is the number of minutes for which the cup has been placed on the table.

(a) Find the value of $$a$$

Initially the temperature of the tea is 92oC.

(b) Find the value of b.

After one minute, the temperature of the tea is 74oC.

(c) Find the value of $$k$$.

(d) Find the temperature of the tea three minutes after it has been placed on the table.

(e) Find the total time needed for the tea to reach a temperature ofof 30oC. Give your answer in minutes and seconds, correct to the nearest second.

### 8.

A-Level

In a remote lake it was noticed by conservationists that a disease was rapidly spreading amongst two species of fish, R and S, which is reducing their numbers. The conservationists calculated that the numbers of each type of fish can be modelled by the functions:

$$r(t) = 9000e^{-\frac{1}{10}t}$$

and

$$s(t) = 6000e^{-\frac{1}{20}t}$$

respectively where t is the time in weeks after the disease was first detected on the 2nd August 2019.

(a) Use the two models to find the number of species R and S on 2nd August 2019.

(b) Find the number of species S after 24 weeks from 2nd August 2019, giving your answer to the nearest 10.

(c) After how many whole weeks will the number of species R first fall below 4500?

(d) Use logarithms and the two models to calculate the value of t when the number of species S will be three times that of species R. Give your answer to the nearest whole number.

(e) When $$t = T$$ the number of species $$S$$ first exceeds that of species R by 500. Use this information and the two models to derive a quadratic equation in $$x$$ where:

$$x=e^{-\frac{1}{20}T}$$

(f) Hence find the number of days after 2nd August 2019 when this difference of 500 fish will first occur. Give your answer to the nearest day.

### 9.

IB Standard

Fifty milligrams of a certain type of medicine has been shown to enter the bloodstream of an adult according to the following equations:

• Rate of entry, $$R = 8 \times 0.93^t$$ mg/min
• Amount in bloodstream, $$A = 49(1 - 0.44)^t$$ mg

where $$t$$ is measured in minutes and $$t\ge 0$$

(a) State the initial rate at which the medicine enters the bloodstream.

(b) Calculate the time it takes before the rate at which the medicine enters the bloodstream is halved.

(c) Find the rate of the medicine entering the bloodstream when there is 25 mg present in the bloodstream.

(d) Sketch both R and A on the same axes. Indicate clearly any intercepts and the equations of the horizontal asymptotes.

(e) Will the patient ever feel the full effect of the 50-milligram dose?

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