# Granny Takes the Train

Science Illustrated - - BRAIN -

The sun is shin­ing, and the sum­mer hol­i­days have just be­gun. Peter is on a 300-m-long train with his grand­mother. When they boarded, the train’s fuel tank was empty, but now it is be­ing filled. The fill­ing takes an hour, in spite of the fact that the speed at which the fuel flows into the tank dou­bles ev­ery minute.

In the mean­time, the grand­mother tells Peter about the time, when she was 19 and had her first baby. Shortly af­ter giv­ing birth, she at­tended a lec­ture along with 99 other new moth­ers. She could clearly re­mem­ber the fash­ion of the time. Of the 100 women, 85 had red hand­bags, 75 wore black shoes, 60 wore a flo­ral dress, and 90 had opal rings. Ev­ery­body had at least three of those things.

Fi­nally, the train sets in mo­tion. The grand­mother talks about her six chil­dren. They were born ex­actly four years apart, and now the youngest is 19. The train passes into a tun­nel. The tun­nel is 300 m long, but the train is mov­ing fast – 300 m per minute – so they are soon back into the light. Shortly af­ter, the train ar­rives at the ter­mi­nal, and Peter fol­lows his grand­mother out onto the plat­form.

1

How much time passes from the front of the train en­ters the tun­nel un­til the back ex­its?

2

How old is Peter's grand­mother?

3

How many of the young women at the lec­ture had brought all four things?

4

How long does it take to fill half of the train's fuel tank?