ABACUS International Math Challenge
for
3rd and 4th graders
December, 1998
A.89. How many whole numbers between 1
and 1998 have the digit 7 within their digits?
A.90. What day would January 1st be, if
you knew that January had exactly 4 Mondays and 4 Fridays?
A.91. A waterlily doubles in size every
day. On the 112th day it covers the whole lake. How many days would it take
for 8 of these waterlilies to cover the lake?
A.92. How would you continue the following
number sequence? Why?
100, 101, 103, 107, 115, 122, 127, ...
A.93. Find all those two-digit numbers
in which the difference of the digits is 3, and if you switch the digits
you get a number that is 9 less than twice the original number.
A.94. Charlie has 5 red, 3 white and 2
green balls. (The balls are identical, except for their colors.) He want
to put them in 2 boxes, where one of the boxes can hold 4 balls and the
other box can hold 6 balls. How many different ways can he place his balls
in these two boxes? (The location of the balls inside of the boxes is not
important.)
A.95. There are a few red and a few green
balls in a box. Without looking, you have to take out 7 of them in order
to have at least one red for sure, and you have to take out 13 of them in
order to have two different color balls for sure. How many red and how many
green balls are there in the box?
A.96. On one of the islands of Magic Kingdom
live the 40-legged animals and the 3-headed dragons. We know that they have
a total of 26 heads and 298 legs. Every 40-legged has one head. How many
legs does a 3-headed dragon have?
Please, send your solutions to: