Short math riddles

100

Can you arrange four 9's and use of at most 2 math symbols, make the total be 100?
99 / .99 or 99 + 9/9
78.55 %

Which number?

What number should appear next in this sequence? 1 5 12 34 92 252 ?
688. Add the two previous numbers and multiply by 2.
78.01 %

Equation riddle

If, Fernando + Alonso + McLaren = 6 Fernando x Alonso = 2 Alonso x McLaren = 6 Then, McLaren x Fernando = ?
3 or 0.75 Explanation: Rewriting the last 2 equations in terms of Alonso, Fernando = 2/Alonso McLaren = 6/Alonso Replacing above values in equation "Fernando + Alonso + McLaren = 6" 2/Alonso + Alonso + 6/Alonso =6 (2 + Alonso^2 + 6)/Alonso = 6 8 + Alonso^2 = 6Alonso Alonso^2 - 6Alonso + 8 = 0 (Alonso - 4) (Alonso - 2) = 0 Therefore; Alonso = 4 or 2 Let's take value of Alonso as 2 Fernando = 2/2 = 1 McLaren = 6/2 = 3 Therefore; McLaren x Fernando = 3 x 1 = 3 Let's take value of Alonso as 4 Fernando = 2/4 = 0.5 McLaren = 6/4 = 1.5 Therefore; McLaren x Fernando = 1.5 x 0.5 = 0.75
77.88 %

Four consecutive prime numbers

Can you find four consecutive prime numbers that add up to 220?
47 + 53 + 59 + 61 = 220
77.53 %

Square root of the number

We all know that square root of number 121 is 11. But do you know what si the square root of the number "12345678987654321" ?
111111111 Explanation: It's a maths magical square root series as : Square root of number 121 is 11 Square root of number 12321 is 111 Square root of number 1234321 is 1111 Square root of number 123454321 is 11111 Square root of number 12345654321 is 111111 Square root of number 1234567654321 is 1111111 Square root of number 123456787654321 is 11111111 Square root of number 12345678987654321 is 111111111 (answer)
77.23 %

Six letters

There is a word and six letters it contains. Take one away and twelve is what remains. What word is it?
Dozens.
77.19 %

Half of two plus two

Is half of two plus two equal to two or three?
Three. It seems that it could almost be either, but if you follow the mathematical orders of operation, division is performed before addition. So... half of two is one. Then add two, and the answer is three.
77.17 %

Subtract 5 from 25

How many times can you subtract 5 from 25?
Just once, because after you subtract anything from it, it's not 25 anymore.
77.13 %

The smallest number

Which is the smallest number that you can write using all the vowels exactly once?
fIvE thOUsAnd (5000).
77.02 %