Substituting into a formula

Question 1

Find the average of 80 and -50 using the formula $x1-+-x2 ˉx = 2$ where $x1 = 80$ and $x2 = - 50.$

Not correct. Choice (a) is false.

Try again, you might have missed the negative sign and calculated $ˉx = 80+-50-= 130 = 65. 2 2$

Not correct. Choice (b) is false.

Try again, you have the wrong sign for your answer.

Your answer is correct.

$80+ (- 50) 30 ˉx = ----------= -- = 15. 2 2$

Not correct. Choice (d) is false.

Try again, you might have only divided one of the numbers by 2 getting $50 xˉ= 80- 2-= 80 - 25 = 55.$

Question 2

If $a = - 3, b = 2$ and $c = - 7,$ what is the value of $4a+ 3b- 2c?$

Your answer is correct.

$4a+ 3b- 2c$	=	$4 × (- 3)+ 3× 2 - 2× (- 7)$
	=	$- 12+ 6 - (- 14)$
	=	$- 12+ 6 +14 = 8.$

Not correct. Choice (b) is false.

Try again, remember $4a$ means $4× a.$

Not correct. Choice (c) is false.

Try again, you may have forgotten to change a sign.

Not correct. Choice (d) is false.

Try again, remember two negatives make a positive.

Question 3

If $x = 3, y = - 4$ and $z = 2$ what is the value of $∘ ---- xy2z,$ correct to 3 decimal places?

Not correct. Choice (a) is false.

Try again, it is the convention that we round up when the next decimal place is a 5 or more.

Not correct. Choice (b) is false.

Try again, remember to take the square root of the whole number $2 xy z$ not just the $x .$

Your answer is correct.

$∘ --2- ∘ -------2---- √ ------ √-- xy z = 3× (- 4) × 2 = 6× 16 = 96 = 9.7979589...= 9.7980$ correct to 4 decimal places,
hence the answer is 9.798 correct to 3 decimal places.

Not correct. Choice (d) is false.

Try again, $2 xy z$ is a positive number.

Question 4

If $P (B) = 0.7$ and $P(A ∩B) = 0.4$ what is the value of $P(A ∩ B) P(A∣B) = --P(B)---$ correct to 2 decimal places?

Your answer is correct.

$P (A ∩ B) 0.4 --P-(B)---= 0.7 = 0.5714...= 0.57 .$

Not correct. Choice (b) is false.

Try again, remember that probabilities must be between 0 and 1 .

Not correct. Choice (c) is false.

Try again, being careful how you round.

Not correct. Choice (d) is false.

Try again, you seem to have subtracted rather than divided.

Question 5

Find $P(B)$ correct to 2 decimal places if $P (A ∣B) = P-(A-∩B)- P (B)$ where $P(A∣B) = 0.3$ and $P(A ∩ B) = 0.2.$

Not correct. Choice (a) is false.

Try again, remember that probabilities must be between 0 and 1 .

Your answer is correct.

We need to solve $0.2 P-(B)-= 0.3$ for $P(B) ,$ that is
$P (B) = 0.2-= 0.6666...= 0.67. 0.3$

Not correct. Choice (c) is false.

Try again, we need to solve $-0.2-= 0.3 P (B)$ for $P(B) .$

Not correct. Choice (d) is false.

Try again, this is not true.


		Faculty of Economics and Business MathQuiz