Numbers: Rounding and estimating

Rounding always helps me when I'm shopping. For instance I've paid £1.10 for this sandwich and I could say £1. Female shopper ...
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Using the discriminant to determine the number of roots

If \(kx^{2}+5x-\frac{5}{4}=0\) has equal roots, then \(b^2-4ac=0\). \(a=k\), \(b=5\) and \(c= - \frac{5}{4}\). \(b^2-4ac=0\) \(5^2 -4\times k \times - \frac{5}{4}=0 ...