# How would one approach question 2.20 of the extra tut questions?

Two annuities will each be payable monthly in arrear for 10 years. Under annuity $$A$$ the monthly payments made in year $$t$$ will be $$11−t$$, while under annuity $$B$$ the monthly payments will be $$1.05t$$ . At an effective rate of $$i$$ per annum the present value of annuity $$A$$ is 5 times that of $$B$$. Find $$i$$ to the nearest 12%
I can find an annuity formula for annuity $$B$$, but I'm struggling to get one for annuity $$A$$?
Hi @michwairish. I've edited your post and added the actual question (this is always better than asking people to look it up in external sources). $$A$$ is a type of annuity known as a 'decreasing annuity'; if you want to read ahead, the formulas usually look something like $$(Da)_{\bar{n|}}$$.