91 = () times () prime

91 = () times () prime

7 times 13

The product of two prime numbers is 91 and the sum is 20. These two numbers are () and ()

The product of two prime numbers is 91 and the sum is 20. These two numbers are (7) and (13)

The sum of two prime numbers is 20, and the product is 91,

13 and 7
20=13+7
13x7=91
A: the number of these two books is 7 and 13 respectively

Take 1 / 4 of two boxes of fruits from the first box and 1 / 5 of them from the second box. At this time, the weight of the remaining fruits in the two boxes is equal. It is known that the total weight of the two boxes of fruits is 62kg. How many kg of fruits are there in the first box?

32
Set the first box AKG and the second box bkg
3/4a=4/5b
15a=16b
a+b=62
The solution is a = 32

If the opposite number of a is 2B + 1 and the opposite number of B is 3A + 1, then A2 + B2=______ ．

The opposite number of ∵ A is 2B + 1, the opposite number of B is 3A + 1, ∵ a = 2B + 1 ∵ B = 3A + 1, the solution is a = - 15, B = - 25. ∵ A2 + B2 = 15

Some money to buy fruit, if you use money to buy apples, you can buy 30 kg, if you buy pears 15 kg. He bought apples, bananas and pears each 5 kg, with 3 / 4 of the total
He bought 5 kg of apples, 5 kg of bananas and 5 kg of pears, which cost 3 / 4 of the total. How many kg of bananas can he buy with the rest of the money?

If you think of money as a share, you can buy 30 kilos of apples, so it costs one sixth of your money to buy 5 kilos
Similarly, one third of the money is spent on pears, so the money for bananas is 3 / 4 - (1 / 6 + 1 / 3) = 1 / 4
There is still 1 / 4 of the money left, that is, you can buy another 5kg of bananas

What is 1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 +... + 1 / N

This formula can be rewritten to get 1-1 / 2 + 1 / 2-1 / 4 + 1 / 4-1 / 8.2/n-1 / N = 1-1 / N = (n-1) / n

If P and Q on the complex plane correspond to complex numbers 1-2i, - 2-4i respectively, find the complex number corresponding to vector PQ
Urgent need

-3-2i

Xiaogang and his father are now 45 years old, and five years later, his father is 27 years older than Xiaogang. How old are Xiaogang and his father today?
We need the formula!

My father is 27 years older than Xiao Gang,
Setting: Xiaogang is x years old and dad is x + 27 years old
x+x+27=45
2x=45-27
x=9
9+27=36
A: Xiaogang is 9 years old and his father is 36 years old

Sequence summation 1 + 1 / 2 + 1 / 3 + 1 / 4 + 1 / 5 + 1/99=?

The sequence composed of the reciprocal of natural numbers is called harmonic sequence. People have studied it for hundreds of years. But so far, there is no summation formula for it, only its approximate formula (when n is very large)
1 + 1 / 2 + 1 / 3 +. + 1 / N ≈ lnn + C
In this problem, we substitute n = 99 to get the result
Sum of primitive sequence ≈ 5.17