Basic Probability: WJEC GCSE Foundation November 2018 Unit 2 Q15

Foundation November 2018 Unit 2 Q15

WJECFoundationCurrent spec4 marksBasic Probability Multiple Events

15. Two fair spinners are divided into quarters as shown below.
One spinner shows the values 10, 20, 30 and 40.
The other spinner shows the values 1, 2, 3 and 4.

Two spinners: the first divided into quarters 40, 30, 20, 10 with its arrow on 30; the second divided into quarters 1, 4, 3, 2 with its arrow on 1

The two spinners are spun and the values shown are added together to form a number.
For example, the diagram above would form the number 31.

Consider all the possible numbers that can be formed.
Calculate the probability that the spinners will form a number that is a multiple of 7.
You must show all your working in order to justify your answer. [4]

Mark scheme

Scheme	Marks	Comments
All possible numbers shown with no extras. (11,12,13,14,21,22,23,24,31,32,33,34,41,42,43,44) OR Clearly justifies that there are 16 possible numbers from 4 × 4 = 16	B2	B1 for at least 10 correct and no more than 4 ‘extras’. 10 + 1, 10 + 2, etc and not added gain no credit.
(Probability multiple of 7 =) \(\dfrac{3}{16}\) or equivalent. ISW	B2	F.T. ‘their list’ only if at least 6 numbers given which includes at least one multiple of seven. OR B1 for x/16 with x<16. B1 for 3/y with y >3. Penalise, −1, any incorrect notation e.g. ‘3 out of 16’. Unsupported 3/16 gains B0B2.