Take a good look at this number: 222221
Is it a prime number?
Answer: No
.222221 = 619 x 359
Saturday 20 December 2014
Matching Pair of Socks
Mammu has 16 pairs of white socks and 16 pairs of brown
socks. She keeps them all in the same drawer, if she picks out three socks at
random what is the probability she will get a matching pair?
Answer: P = 1. She is certain to get a pair.
A mixable Numbers
The numbers 220 and 284 are known as amicable numbers. The
reason is the sum of the proper divisions of 220 equals 284 and what is even
more interesting is the sum of the proper divisors of 284 equals 220.
So far about 100 pairs of amicable numbers are known. Can
you find some in four digits?
Answer: 1184 - 6368, 5020 – 2924,
2620
- 5564, 6232 -
1210
Playing Children
A group of boys and girls are playing. 15 boys leave.
There remain two girls for each boy. Then 45 girls leave.
There remain five boys for each girl. How many boys were in the original group?
Answer: 40 boys.
Let G represent the number of girls in the original group
and B the number of boys in the original group. Then we have:
G / B -15 = 2/1 and G – 45 / B – 15 = 1/5
Then G = 2 (B- 15)
5(G -45)
= (B – 15)
Solving the simultaneous equations above we get:
B = 40 and G = 50
Boy or girl
Vikram Chadda has two children, and at least one of them is
a girl. What is the probability that both children are girls?
Answer: There are
three possible outcomes:
G - B, B- G or G – G. Since only one of these three is girls
the probability is ⅓
Solving Problems
Romila appeared for a maths exam. She was given 100 problems
to solve. She tried to solve all of them correctly but some of them went wrong.
Any how she scored 85.
Her score was calculated by subtracting two times the number
of wrong answers from the number of correct answers.
Can you tell how many problems she solved correctly?
Answer: She
solved 95 problems correctly
Let us assume W = Wrong and R = Right
R - 2W = 85
R + W = 100 / -3W= -15
W = 5
W = 5
R = 95
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