Questions

The concrete slump recommended for beams and slabs is 30 to 125 mm.

Magma is molten rocks beneath the earth's crust. Hot springs are heated geothermally by underlying magma.

Bond breaking is an endothermic process.

Hence, bond breakage needs an amount of energy and uses some energy based on the strength of the bond to break the bond.

The exact time taken by the earth for single rotation on its own axis is 23 hrs 56 min 4.09 sec.

 4600 million

Let the missing numbers be x, y, a and b

x + y = 8 ---- (1)
a - b = 6 ---- (2)
x + a = 13 --- (3)
y + b = 8 ---- (4)

2x + a + y = 21 --- From (1 & 3)
a + y = 14 ----  From (2 & 4)

Substitute (2 & 4) in (1 & 3)

2x + 14 = 21
2x = 7
x = 3.5

From (1) ---> 3.5 + y = 8
=> y = 8 - 3.5 = 4.5

a + y = 14 => a = 14 - y = 14 - 4.5 => a = 9.5
From (4) ---- y + b = 8 => b = 8 - y = 8 - 4.5 = 3.5

Hence,
x = 3.5
y = 4.5
a = 9.5
b = 3.5