11 plus sample question

[n1tram]

My son is doing a sample 11 plus maths exam. The last question is below, can anyone help me by explaining the answer.

A milkman and a baker deliver to the same house.
In a period of 28 days, the milkman calls every second day and the baker every third day.
They meet at the house twice in the first 7 days.

How many more times do they meet during the 4 week period?

I know the answer but not the formula to solve it

[scrunge999]

They can only meet on multiples of days that are a product of the periodicity of each visit. They meet every (2 x 3) days, i.e. every 6 days:

1. M B
2. _ _
3. M _
4. _ B
5. M _
6. _ _
7.M B

The only way they can meet twice in the first week is if they meet on the 1st and the 7th days. They next meet on the 13th, then the 19th, then the 25th. So they meet 6 times during the 28 days.

Being pedantic however, this assumes that they both arrive at the same time each day.

[DTCwordfan]

I hope the customer was making bread pudding on the days that they did meet.

[scrunge999]

5 times!

D'oh...

[Old_Geezer]

They both know the lady of the house and so are there most of the day ;-)

[Noraq]

Lol..Oldgeezer..I was thinking that! =)

[The Builder]

I can't find any formula, except that they meet every third odd numbered day ...... both starting on one......
Five in total

[n1tram]

Many thanks everyone for your answers, thanks scrunge999 for explaining the answer

[factor-fiction]

They meet on days 1, 7, and then again on days 13, 19 and 25 so the answer is 3.

As others have said they meet every 6 days. To have met twice in week one they must have met on days 1 and 7.