Grow $200 by 15%, what's the new value?

Question

Applying a growth rate is base plus the percentage of the base. Solve in your head. What is \200 increased by 15\%? Aim: under 8 seconds.

Accepted Answer

Compute 15\% of 200, then add it on. 10\% is 20, half of that (5\%) is 10, so 15\% = 30: 200 + 30 = 230. So the new value is \mathbf{\230}. Equivalently, multiply by 1.15: 200 	imes 1.15 = 230. Takeaway. Growth of p\% means multiply by 1 + p/100. Build the p\% from a 10\% chunk plus a 5\% half-chunk, then add to the base.

Grow $200 by 15%, what's the new value?

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