Multiple Events: WJEC GCSE Intermediate November 2018 Unit 2 Q7

Intermediate November 2018 Unit 2 Q7

WJECIntermediateCurrent spec4 marksMultiple Events

7. 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: one with 10, 20, 30, 40 with the arrow on 30; the other with 1, 2, 3, 4 with the 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.