S1 January 2005 Q1

EdexcelOld spec6 marksProbability

1. A company assembles drills using components from two sources. Goodbuy supplies 85% of the components and Amart supplies the rest. It is known that 3% of the components supplied by Goodbuy are faulty and 6% of those supplied by Amart are faulty.

(a) Represent this information on a tree diagram. (3)

An assembled drill is selected at random.

(b) Find the probability that it is not faulty. (3)

Scheme	Marks
Tree	M1
0.85, 0.15	A1
0.03, 0.97, 0.06, 0.94	A1
	(3)

Scheme	Marks
\(\mathrm{P}(\text{Not faulty}) = (0.85 \times 0.97) + (0.15 \times 0.94)\)	M1,A1
\(= 0.9655\)	A1
	(3)
	(6 marks)

Notes