Mr. Li bought 20 watercolor pens and pens at a total cost of 100 yuan, 3.5 yuan for each watercolor pen and 5.5 yuan for each pen How many watercolor pens and pens do you have? Arithmetic (hypothesis)

Hypothesis: all bought watercolor pen
Pen: (100-20 × 3.5) / (5.5-3.5)
=（100-70）÷2
=30÷2
=15 (pieces)
Watercolor pen: 20-15 = 5
A: there are 15 pens and 5 watercolor pens
Hope to adopt!

The decimal point of a decimal point is moved to the right by two digits, which is 198 more than the original number. The original number is ()

The original number is 198 (100-1) = 2

A car travels 45 kilometers per hour, B car travels 60 kilometers per hour, after 2.5 hours to meet, find the distance between the two places

(45+60)*2.5=105*2.5=262.5

If a, B and C are trilateral equations of triangle ABC, a (1-x ^ 2) + 2cx + B (1 + x ^ 2) = 0 has two equal real roots, and 3C = 4A, find Sina + sinc

If the equation has two equal real roots, delta = B ^ 2-4ac = C ^ 2 + A ^ 2-B ^ 2 = 0, then a ^ 2 + C ^ 2 = B ^ 2, so triangle ABC is right triangle, angle B is 90 ° and 3C = 4A, then B = (5 / 4) C a = (3 / 4) C can

The distance between a and B is 360 km. How many hours does it take for the car to complete the whole journey when the car starts from a to B and exceeds the midpoint of 20 km in 2.5 hours?

Speed = (360 × 1 / 2 + 20) △ 2.5 = 80 km / h
Whole course = 360 △ 80 = 4.5 hours

Given X: Y: z = 1:2:3, then the value of fraction x2 + Y2 + Z2 divided by 2XY + 3yz-4xz is
X2 is the square of X, and so on

Solution X: Y: z = 1:2:3 let x = k, y = 2K, z = 3K ■ (X & # 178; + Y & # 178; + Z & # 178;) / (2XY + 3yz-4zx) = (K & # 178; + 4K & # 178; + 9K & # 178;) / (4K & # 178; + 18K & # 178; - 12K & # 178;) = (14K & # 178;) / (10K & # 178;) = 7 / 5

A and B start from a and B at the same time and run in opposite directions. As a result, they meet at a distance of 60 km from the midpoint. It is known that a runs 20% more than B. how many meters are there between a and B
PS: it's best to use the equation

Let B travel x kilometers, then a travel (1 + 20%) x kilometers
（1+20%）X-X=60×2
20%X=120
X=120÷20%
X=600
Therefore, the distance between a and B: 600 + 600 × (1 + 20%) = 1320 km

It is known that the definition field of function f (x) is r, and for any a and B belonging to R, f (a + b) = f (a) + F (b), and if x > 0, f (x)

f(a+b)=f(a)+f(b)
Let a = b = 0
f(0+0)=f(0)+f(0)
f(0)=2f(0)
f(0)=0
Let B = - A
f(a-a)=f(a)+f(-a)
f(0)=f(a)+f(-a)
f(-a)=-f(a)
Odd function

On a map with a scale of 1:2000000, the length of a and B is 8 cm
How many centimetres is the distance between them?

8 △ 1 / 2000000 × 1 / 4000000 = 4cm

If there is a real number x and cos α = x2 + 12x holds, then the value range of real number x is ()
A. {- 1, 1} B. {x | x ＜ 0 or x = 1} C. {x | x ＞ 0 or x = - 1} D. {x | x ≤ - 1 or X ≥ 1}

∵ Cosa ∈ [- 1, 1] ∵ 1 ≤ x2 + 12x ≤ 1, that is: x2 + 12x ≤ 1x2 + 12x ≥ − 1 ∵ x = 1 or X ＜ 0x = − 1 or X ＞ 0 ∵ x = 1, - 1, so select a

Mr. Li bought 20 watercolor pens and pens at a total cost of 100 yuan, 3.5 yuan for each watercolor pen and 5.5 yuan for each pen How many watercolor pens and pens do you have? Arithmetic (hypothesis)