help needed with probability question, age question and 'zap

[Charlotte]

I am struggling with this type of question:
I can explain P of 1 green being 7/18 etc but have become stuck

1) there are 6 red, 7 green and 5 blue beads in a bag. What is the smallest number of beads taken out before i can be sure of getting at least 2 of each colour?

Ans. 15

2) In 6 years' time Mira will be twice as old as she was 3 years ago. How old is she now?
Ans. 12
why can't I do
now x-6 = 2(x+3)

x-2x = 6+6

-x = 12

3) what is the quickest way - what are they testing in this sort of question

a number can be zapped by mulitplying its digits so 235 zapped is equal to 2x3x5 = 30.
what is the smallest number which can be zapped to give 24?

Many thanks for your help; i have tried or hours especially with probability and age question.
feeling quite out of all this

[stevew61]

1) there are 6 red, 7 green and 5 blue beads in a bag. What is the smallest number of beads taken out before i can be sure of getting at least 2 of each colour?

Ans. 15

In a way you are looking for the worst result, so you are sure to get two off each colour. Imagine it's a game and the balls are being drawn out, worst case,

7 greens, followed by
6 reds, followed by
2 blues

Total 15

You don't always have to do a mathematically proven answer, just try to work out a solution to the problem.


steve

[stevew61]

In 6 years' time Mira will be twice as old as she was 3 years ago. How old is she now?
Ans. 12
why can't I do
now x-6 = 2(x+3)

x-2x = 6+6

-x = 12

I would use M+6=2(M-3) expand brackets
M+6=2M-6 add six to both sides
M+12=2M take M from both sides
12=M


steve

[yoyo123]

number 3 . I'd look at the factors of 24

then choose the 3 which would give lowest 3 digit number.

My guess is that they are testing knowledge of factors and problem solving skills. I take it that this is standard format, would be a bit of a giveaway question in multiple choice!

[Charlotte]

Thanks steve and yoyo123 - has helped - i am sure there will be many more unless maths improves :