Math Club

Riddles

100

What gets smaller every time it takes a bath?

soap

200

I'm sweet and cold with a stick to hold; a treat on a hot day, worth more than gold. What am I?

A popsicle

300

What word contains 26 letters but only has three syllables?

Alphabet.

400

David's father has three sons: Snap, Crackle and _____?

David

500

What is more useful when it is broken?

An egg.

Mental Math

100

12 x 11 in your head

132

200

47+68+29 in your head

144

300

36×25+48×25

2100

400

74 x 66  (20 seconds)

4884

500

What’s 15^2−14^2 without a calculator?

By difference of squares: (a+b)(a-b)=a^2 - b^2

29

Algebra

100

2x+5=17

x=6

200

3y−7=2y+5

y=12

300

4(x−2)+3=3(2x+1)

x=-4

400

Find x and y:

2x+y=10

x−y=4

x=14/3 y=2/3

500

5^x+1 * 25^2-x = 5^5

 x=0

Sequences

100

Is this an arithmetic or geometric sequence:

3, 6, 12, 24, 48...

Geometric

200

What is an expression following the sequence?

3, 5, 7, 9, ...

2n+1

300

What is the 10th term of the sequence: 3,7,11,15,… 

39

400

Find the sum of all single-digit numbers: 1+2+3+⋯+9

9 x 5 = 45