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Each day Chen buys pasta or a sandwich. Where Pasta costs £3.20 and Sandwich costs £2.75. For 45 days, the relative frequency of Chen buying a sandwich was one fifth. Altogether, how much did he pay?

Firstly work out how many days Chen bought a sandwich, which was one fifth of 45 days. So 45/5 = 9. We then multiply 9 by the cost of a sandwich, 9 2.75 = 24.75. The remaining days Chen must have bought Past...
KM
Answered by Kyle M. • Maths tutor
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Explain why the contraction times of the atria and ventricles in the heart differ.

The atria have a shorter contraction time as the ventricles as they only need to pump blood into the ventricles. The contraction time of the ventricles is longer as they need to pump blood through the aorta ...
PK
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Prove that (4x–5)^2 – 5x(3x – 8) is positive for all values of x.

To begin we need to simplify the expression. First we multiply out (4x–5)^2 to get 16x 2 +40x+25 and then we multiply out 5x(3x – 8) to get 15x 2 -40x. This makes the whole expression 16x 2 +40x+25-(15x 2 -4...
HW
Answered by Hannah W. • Maths tutor
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Find the values of x where the curve y = 8 -4x-2x^2 crosses the x-axis.

A curve crosses the x-axis when y=0, if we put that into the equation above we get the quadratic equation 0=8-4x-2x 2 . The solutions to this equation are the values of x where y=0, which is the same as sayi...
HW
Answered by Hannah W. • Maths tutor
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What factors affect the lattice enthalpy of an ionic solid?

We must remember that negative energies (in any context) generally represent energetically stable configurations and as the energy of a system increases, it will become more unstable. Firstly, ionic size aff...
SD
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